Depends how big the Africans are really.
I kept a crayfish through about 4 moults in a 46G tank - brought the cray back, which was still in good health then - because I considered it was getting too much stick from the cichlids and I basically never saw it except at night; it was surviving but not thriving.
In a big enough tank, together with plenty of rockwork, I think you can give it a shot and have a good prospect of success. The crayfish will definitely try and go after anything smaller than 3 inches, but I found that mine, which were all 3 inches or more, were well able to escape him, and in fact beat him up, which is why I brought him back.
I think in a bigger tank there would have been much less interaction between them. If memory serves there is a species of freshwater crab native to Lake Malawi, so its not that crazy a mix at all.