The Rozlamists seem to have been basically a pro-Bolshevik faction in the SDKPIL. You can read a bit about them in the editorial notes to Lenin's 1912 article supporting them, as against Rosa Luxemburg/Tyszka:

wikirouge.net

Rosa Luxemburg and the Polish “Partei” Vorstand in Martov’s Wake

Lenin's article was first published only in 1964. By the way, as to Radek's expulsion, we read:

A commission to review the court’s decision was set up in Paris in early September 1913 on the initiative of the Bureau of the sections of the Social-Democracy of Poland and Lithuania abroad (Rozlamists). Lenin supported the review of the Radek case, for he believed that the charge against Radek was the outcome of the sharp struggle which the Chief Executive was waging against the Rozlamists. The commission worked for five months and arrived at the conclusion that there had been no ground for committing Radek to trial by a Party court and expelling him from the Party. It proposed that Radek should be considered a member of the Social-Democracy of Poland and Lithuania and of the RSDLP.

Lenin's article was translated into German by Malecki (Малецкий, Александр), who was himself a Rozlamist. This is the note about him in Lenin's CW:

Malecki, Alexander Mavrikievich (1879–1837)—Social-Democrat, joined the revolutionary movement in the late nineties. In 1906 elected to the Executive of the Social-Democratic Party of the Kingdom of Poland and Lithuania. After the split in Polish Social-Democracy in 1912 he was one of the leaders of the “Rozlamist” opposition, which stood closest to the Bolsheviks. Delegate to the Basle Congress of the Second International in 1912 and the Brussels meeting of the R.S.D.L.P. in 1914. From 1921 he worked in the publishing business and as a teacher.

His name is also spelled Maletsky or Maletzky. He wrote a few articles in the early 1920s in the Communist International that are available in English, eg he wrote a 1923 review of an issue of the theoretical organ _Vestnik of the Communist Academ_y (whose index I posted on libcom): archive.org

In that review he came to talk about an article (by Dvolaitsky) that criticised Rosa Luxemburg's theory of accumulation. Now, as having been an "opponent" of Luxemburg earlier in the SDKPIL, you perhaps would expect that Maletsky disregards her theory. But that is not the case. He actually comes out in defense of her theory, despite his political opposition to her earlier. So in my opinion this testisifies to his ability to be objective. Here's Maletsky's support of her theory:

We venture to bring to the neader’s notice an article by Dvolaitsky, “The Theory of the Market,’’ in view of the important bearing which the problems of accumulation have on the practice and theory of Communism. Dvolaitsky speaks for and against the theories of Luxemburg, as expounded in her well-known works, “The Accumulation of Capital’’ and ‘‘Anti-Critique,” and against Thalheimer, who declared at the Fourth Congress of the Comintern that Rosa Luxemburg’s theory should be made the basis of the Communist programme and the Communist manifesto of 1920. We shall not argue the matter here with Dvolaitsky, but merely limit ourselves to a few remarks. Dvolaitsky disagrees with Thalheimer, who contends that the Communists who repudiate Luxemburg’s platform ‘‘give theoretical proof of the impracticability of Socialism and open a way for themselves to the camp of the bourgeoisie”. Dvolaitsky justly points out that the Russian home-bred Marxists, including Lenin, have produced a theory distinct from that of Luxemburg, and nevertheless remained in the ranks of the struggling proletariat. Dvolaitsky, however, forgets two things: ⁽¹⁾, the fact that when the Russian Marxists wrote about the accumulation of capital, Imperialism was not what it is now and the direct revolutionary struggle against Imperialism was not the immediate problem of the proletariat; ⁽²⁾ that the chief opponents of Luxemburg among the West European Socialists happened to be in the camp of the bourgeoisie. - Furthermore, the Russian Marxists conducted their controversy with the Narodniki, and not with Rosa Luxemburg. Comrade Dvolaitsky’s reasons why the Russian Marxists gave little attention to the theory of Luxemburg are incorrect. According to Dvolaitsky, this was partly because Rosa Luxemburg’s chief works became accessible to the Russian Marxists only as late as 1921. I think there are other reasons as well. Luxemburg’s work appeared in 1913, and was instantly followed by replies from Bauer, Eckstein and Pannekoek. Almost all the prominent Russian revolutionary Marxists were abroad at the time and naturally were fully able to make themselves acquainted with Luxemburg’s writings. If they made no comments, it was first of all because the problem itself was a very complex one, and secondly, even those Russian revolutionary Marxists who probably did not agree with Luxemburg’s theoretical arguments, refrained from stepping forward against her for tactical reasous in view of the revolutionary significance of her position and in order not to support the opportunists who held that the economic collapse of Capitalism was not inevitable. I recollect how Comrade Kamenev, in a private conversation, expressed the same opinion and averred that Luxemburg’s book is of vast propaganda value. Dvolaitsky may learn for himself that even now there are Russian comrades who take Luxemburg’s theory precisely this way.

I may refer to No. 21 of the ‘‘Communists’ Companion” (‘‘Sputnik Kommunista’’) containing a review by Schwartz (which, by the way, is an answer to the first attempt by Dvolaitsky in the “Krasnaia Nov” of June, 1921, to refute the theory of Luxemburg by means of workers’ credit and the state taxation) and an article by Bessonov, which gives full support to Thalheimer and flatly announces that ‘‘the great revolutionary significance of Luxemburg’s theory consists precisely in the fact that she precludes every possibility of reconciling the contradictions of capitalism prior to the transition to Socialism and Communism.”

Thus, in my opinion, the revolutionary significance of Luxemburg’s theory is incontestable and Dvolaitsky’s objections are not convincing. Further, if, as Dvolaitsky says, the accumulation of capital in a purely capitalist environment is theoretically feasible in practice (as he himself asserts in the ‘‘Krasnaia Nov,” and which he seems to have forgotten in the present article) accumulation confined solely to capitalist environment would be possible to a very small degree. ‘‘German capitalism,’’ states Dvolaitsky in the “Krasnaia Nov,’’ would have achieved the successes it did only in the course of a few centuries, while French capitalism would have died out together with the French population. At the same time, full-blooded capitalism objectively requires a wide scope and the whole world inevitably becomes transformed into the arena of its incredible expansion. Precisely from this angle both of Luxemburg’s cited works threw a vivid light on the problem of imperialism.”

If this is so, does it not imply that Luxemburg’s theory contributed something new towards the explanation of imperialism, even from the point of view of Dvolaitsky himself, of the Dvolaitsky of the “Krasnaia Nov”? As to the essence of Dvolaitsky’s objections, I am not able here to subject them to a detailed analysis. I am sure that Comrade Thalheimer will answer Comrade Dvolaitsky. I consider that Dvolaitsky’s first attempt in the ‘‘Krasnaia Nov” and second attempt in the “Vestnik” to refute the theory of Luxemburg are unsound. Neither “Workers’ Credit” or any credit is a reply to Luxemburg’s query as to the possibility of expanding production in a purely capitalist environment. Now Comrade Dvolaitsky advances credit on the one hand and the striving of the capitalists for maximum profits, not profits in general on the other, as the explanation of the problems of imperialism. This merely puts the question off, but does not elucidate it. We must be grateful to Comrade Dvolaitsky, however, for making these problems a current topic, even if he has failed to solve them. We hope that his article will call forth a fruitful discussion.

Maletsky also was listed as editor with Frolich of a Luxemburg volume in Russian in the 1920s. I don't find much mention of him later.

I was already aware of the above-mentioned article of Schwartz (and I listed some other writings of Schwartz on the former ICC forum), but it's not online.

On the thread 'Capital's inherent contradictions' I defended Luxemburg's theory of accumulation. I maintain that her critics have not refuted her. That controversy involves an issue of measuring national income, which recently William Jeffries has engaged. That is, GDP.

Some comrades (like Link) just take this figure at face value, as an indicator of accumulation. Jeffries believes that such figure of GDP when it is calculated eg for the Soviet Union, does not indicate capital accumulation (as he does not believe the USSR was capitalist). I don't wade into that separate debate, but my point in general is that GDP is not an indicator for accumulation (in the precise Marxist sense, that Luxemburg had).

They take a date, say GDP for 2010 (or whatever), then another date, say GDP for 2015, see that the number grew, and so declare accumulation is happening (contra Luxemburg). I won't gripe further about such simplistic arguments now though, unless others want to debate it.