I have mine with a senegal bichir, a pleco, pictus catfish, and 3" african cichlids... its not natural but they all get along. DO NOT put any fish that are less than half the size of the rocket gar in with it as it will get eaten. I had some rather fast chinese algae eaters and the gar ate all that were 2" or less... hes good at it.
Do not underestimate that fish... rocket gars have the ability to stretch their jaws to accommodate for the fish, they can eat something that is actually wider than their head.