Keyholes have been considered as being "THE MOST PEACEFUL CICHLID of all"!! They get along fine with large peaceful cichlids such as Jurapari's, Severums, and Festivums. And some say can be trusted with very small rasboras and tetras. Males can become aggressive during breeding, however, they do little or no damage to other keyholes and tend to ignore smaller tetras and corydoras completely, even ones found swimming over the breeding site.
I imagine tank size plays a role as well, they are timid fish so give them lots of hiding spots.