Welcome back Grundulis!
What are you looking to accomplish by adding a species like this? Just more diversity?
With adequate predators present (here we'd suggest largemouth bass for control), they shouldn't overpopulate. But you also probably won't see any benefit to them either. Stocking at such small sizes, they'll be gobbled up pretty quickly.
If for some reason the predators weren't able to knock them back, bullheads can create problems. Their spawns are large, they create muddy water by scavenging around the bottom of ponds, and can be pesky little bait thieves when fishing for something else.
