Bass are very predatious! I dont think there is much they wont eat. They'll eat baby ducks, snakes, small turtles, muskrats, mice, bullfrogs, birds. Pretty much anything they can get in their mouths and down their throats. And
YES they will cannablize each other.
I would ask the owner to stock some type of forage in there for the bass to feed on continually.
Heck, with permission first go to the creek and catch a bunch of bluegill and bullhead Catfish to stock it with.
Bass love those things! I caught a 4 pound Bucketmouth last summer with an 11 inch bullhead in it's gullet.
The only time bluegill, sunfish, and bullheads will ever over run a pond and become stunted is when there aren't enough predators in the pond or lake to keep the numbers low. There has to be a healthy predator prey balance. The size of bluegill and bullheads in a pond or lake can be a good indicator of a healthy largemouth bass population. Smaller sunfish and bullheads are very vulnerable to largemouth bass predation, which decreases their abundance and increases their average size. If a pond or lake owner is a bluegill or bullhead aficionado, largemouth bass abundance can be managed to produce BIG jumbo gills and bullheads. Prey species also need enough cover to escape from being totally annihilated by the bass. That way they can recharge the food chain for the bass.
Pictured above are small channel and bullhead catfish in the gullet of largemouth bass. 
