While I normally suggest keeping CAs with CAs, SAs with SAs, and Africans with Africans, it can be done, as long as the Africans are of a similar size. The water parameters, are actually more similar between Central America (Jack Dempsey) and the African Rift Lakes, than they are between Central and South America. The natural environment that the Jack Dempsey comes from tends to have a medium high
pH, and is relatively hard.
I currently have seven young adult (5" to 8") JDs in a 100 gal with six Africans. They are kept on an aragonite sand substrate to keep the pH and hardness high. The JDs are doing fine, in fact I had a pair spawn two weeks ago, and got about 500 fry out of it.
Here's a pic of two of the JDs with the Africans.
They have been together since July 2008, and as you can see, everyone has all their fins and scales.
Good Luck,
Mark