I'll probably be shunned forever for this, but I have had good luck mixing Tang. Africans with Malawi. Check my user page for what I have now. I've run the whole spectrum--mixed species Malawi only, mixed Tang. only, species only Mbuna, etc etc. I used to keep 5 tanks 50 gallons and up so my possibilities were endless. Well, I fell in love with certain species over the years and time and money and children brought me to my single 55 gallon. So I chose to mix Tang. and Malawi cichlids. I do try to keep all omnivores so that none of them suffer from the other's dietary needs.
So my answer is go for it--I have never had any problems. Just provide what they all need in the lines of food and shelter. The water chemistry lines all cross (ph, temp, etc) so choose the best middle ground. Pick fish with the same diets (a herbivore will suffer and eventually die from high protein diets of omnivores) and have fun.