Lets remember, Common Sense should apply!!! (though I think we "Americans" maybe be running a bit low on it)
Will a mbuna-Gourami tank work forever? Depends; most likely no. Short term, possibly.
I would not recommend buying a fish to "experiment" compatibility. If you don't have a backup plan for a fish, DON'T BUY IT!
As a perfect case to this (actually pretty similar to this guy's case), I have a pink kissing gourami in a 40 gallon tank with 2 inch mbunas. They get along fine, never seen the mbuna ever chase "pinky" (in fact their afraid of him). Another case, I have a 120 with Africans along with a few Americans (severum, convict).