I can see a few reasons why its probably unlikely.
1) The US - what are they doing while minor European powers go rampaging through their sphere of influence?
2) The terrain was awful, and the Belgians have no experience fighting in it (Ok the Congo might be similar, but the units there are going to stay there).
3) The Belgian interwar army, if it was anything like the Dutch (which I know a bit more about), was being systematically dismantled by this point in an attempt to balance the budget. Any money they do have will be channelled towards defending themselves against Germany.
4) How are they getting there? They don't have the naval capacity, even if they did none of the protagonists has any coastline for them to land. I doubt any of the other SA nations would be too keen to allow a European army access to one of their ports.
5) Belgium will probably be kicked out of the League of Nations, and it won't be able to count on Britain and France defending it in the future.
Apart from that, I can't see any problem.