i would keep the rubberlip outta the mbuna tank, but the common should do just fine especially if everybody is still small. i have many differant ploecos in with my mbuna right now with no problems. a royal, 4 bns, and an emporer.
Since both the African ciclids (mbuna) and the pleco are babies, would that make a difference in them getting along? Growing up together?? Maybe they would be used to eachother and not attack? (wishful thinking, I know...)
It will work for a while but once the fish hit maturity all bets are off. Like I said it may work, it may not. It's pretty hard to predict once the mbuna get larger. I've had fish live together for over a year then suddenly go on a killing spree.
One of the best combos are infact that, but depending how big your tank is determines what you can add In general if your keeping africans you could and infact should have enough room for something like a bristle nose.