Sharly
Your assumption of the date of your pic being dated after 3/1901 - based on the black arm bands - is very hard to argue against. The inscription on the back of the pic is interesting; firstly because of the date (1900), secondly where the pic was taken (Natal), and thirdly the words "recruiting officers".
Colonial Australian units for South Africa in 1899-1900 were recruited at home and I very much doubt they trawled locally in SA for recruits until later. Moreover, they were not on the Natal front in 1900; being occupied elsewhere in Rhodesia and Cape Colony. So the date "1900" is definitely suspect. Whoever wrote it made a mistake. So we come back to the words "recruiting officers".
To diverge a little, initial recruiting at home for the Boer War colonial Australian contingents was usually over-subscribed for several reasons - and the same probably also applied to contingents fron NZ and Canada. Here in OZ, and especially in the later phases of the campaign, disappointed would-be recruits often journeyed to SA as horse handlers or indulgence passengers; on the understanding that they enlisted in one or another of the locally raised units on arrival. No one really knows how many there were - unless a man disclosed his home address on his enlistment papers.
When the seeker-after-adventure arrived at one of the sea ports in SA Durban in Natal or Cape Town, there were waiting recruiting officers for the ILH, Brabant's, SALH, etc., ready to snap up a likely lads for five bob a day each and all found. Thus, two aspects of you pic's notation fit into such a scenario. "Recruiting Officers" and "Natal".
Regarding the ID of the uniforms in your pic, I cannot really offer much more than I already have. Should the recruiters have included an officer from the QMI, I would have thought he would have sported Emu Feathers in his pugaree. I can't help much about distinctive headgear for the S. Aust MR, Bushmen or IB.
Let me know what you think about the scenario I have proposed. What a pity we will never know for sure.
Regards
IL.