For the record, it's not what I'd normally do in a display tank that I wanted to look "right", but temporarily in growout or overflow tanks I've had some 'weird' combinations. Might be juvies, extras, misfits, etc. until I sell or move some of them, rearrange tanks, or whatever.
For example, I have a breeding group of kapampa fronts and I've kept extras in overflow tanks with severums, guianacara, geos, etc... come to think of it I knew someone who kept frontosa and geos together in his main tank, just because he liked both fish-- weird maybe, but it worked.
A lot of cyphotilapia would be compatible in temperament with a number of SA species, actually. (Again, weird as it sounds, I've even seen a couple of people keep them with discus.) There are other African species I've had that would work with a number of new worlds in terms of temperament. But it needs to be the right species, I wouldn't get a bag of 'mixed Africans' and just throw them together with a firemouth.
The bottom line is whether or not you like the idea is not the same as whether or not it can be done.