You might like to see Apollon Davidson and Irina Filatova, The Russians and the Anglo-Boer War 1899-1902. They are two Soviet historians who have written at length on this subject both before and after the collapse of the communist regime. Best of all, I found the first 80 or so pages of their book on the web only yesterday.
On 26 June 1900, on a ridge near Lindley in Free State, Captain AEM Norton DSO, 4th South Australian Imperial Bushmen, shot dead a Russian in the uniform of a Russian naval lieutenant. The shot was fired over 1,200 yards. Norton was my grandfather.
A fortnight ago, in the Pretoria cemetery, I stumbled over the grave of Lt Boris von Strolman, killed near Lindley on 26 June 1900 and reinterred in Pretoria a few years later at the request of his mother in Moscow. From other evidence I'm confident this is Norton's man. On p.40 Davidson and Filatova state that Strolman, presumably a member of the Baltic German nobility which had served the Russian state for centuries, was both a volunteer and an observer for the Russian armed forces. So too was a Lt Alexander Guchkov, later Minister for War in the ill-fated Provisonal Government in 1917.
Thank you for providing some little known but very interesting information. It seems that the Boer War had a nearly endless number of unusual participants who engaged in numerous incidents in obscure places. It takes a researcher such as yourself to bring this information to our attention.