I personally don't know if there is a canon or a scholarly profession that debates the legitimacy of ADF. I do know that ADF is a real genre of documentaries. There is research that can be done on this. The topics range from wildlife safaris, to leaders of African nations. There are many documentaries about Nelson Mandela and The African National Congress of South Africa. There are film festivals held is South Africa explicitly geared towards documentary film. So while I don't know for sure if scholarly discourse of ADF, I'm sure there maybe if film festivals are being held throughout Africa. There is also the West African Documentary Film Forum that is on-line. So in the real world and in cyberspace people are talking about Documentary film from Africa.
We all come from diverse backgrounds. We have unique gifts that we can give the world from our different life experiences. I write that to say that yes someone of African descent can produce documentary films about non-African societies. It's not different than white American or European anthropologist studying indigenous groups in Africa and making films about them. These videos sometimes in appear in French, Dutch, or Spanish, but still they are ADF's. Having films translated into a different language doesn't take away from the Africaness of the films topic or that it was filmed in Africa. Sometimes it's necessary to change the language for the audience you are trying to reach.
So for me I think there is a genre known as African Documentary Film, that can teach and inspire others to travel to the continent of Africa in search of a rich history and culture that is often thought of negatively in the Western world.