You can get the licence and work for a South African company. You may not apply your skills within the borders of South Africa unless you get the permit. In other words you can go on 'contract' in another African country. Considering the fact that there are already American registered aircraft operating in Africa requiring FAA rated pilots one would wonder just why you would then go to all the hassle of getting a SA licence to start with. My guess would also be that the number of ZS register aircraft in Africa is diminishing.