Alligators should not be with dfish you don't want them to eat. Also, alligators should have a level of water where they can breathe without undue stress and effort, which, with a juvenile alligator is not a level of water suitable for fish "you want to keep alive".
The ph for african cichlids is way above the ph an alligator is best kept in.
This ph, if not unduly important for the aligator is of utmost importance to the mata matas. They only live well in acid water, tottally unsuitable for african cichlids.
If an alligator can try, and manage to, climb a rock ( NEVER SWIMMING ), a mata will only be able to breathe if its extended neck reaches the surface.
Mata mata are awesome turtles to have (as are allis and snappers generally ) if you dedicate yourself to their needs and study the best conditions to keep them in..
I would never advise such a turtle as an impulse.