I have never kept Keyhole Cichlids, but I would think it might work. I have seven Bandit Cichlids (G. Geayi) growing out along with a bunch of G. steindachneri in a 125 and they get along just fine. It is possible the keyholes would beat up the bandits, but it might be worth a shot.
I would not be concerned with aggression from the keyholes. I keep mine with small tetras and angels and have never had a problem. I agree with Matt in that the geos may become bullies to the keyholes. Maximizing territories and breaking up line of sight should help defuse aggression.