Thank you, gents. Yes, Pat - Western Front only. Thanks for the photo of the IR 25 chap. Have managed to find the original photo of black German allegedly being taken prisoner by the French.
The Hussar theory is a bit troublesome. I think there might be some duplication going on. Suggestions are that there was more than one black drummer, and the names given are variously Tambow, Mambow, or, unfortunately, Sambow. It would be a very small world if there were two black cavalry drummers, so I think some confusion has crept into the proceedings. Investigations continue.