Sam, I have arrived on non-scheduled a/c into Kenya, Tanzania, Mozambique, Namibia and South Africa, none of which were a problem. It depends more on the airport you are flying into, IOW you have to arrive at a designated port of entry. This can be waived in some instances, but I would certainly not count on it in planning. In any case, travel by light a/c is pretty common in Africa, so you won't be the only one doing it.