They might be alright if you do have it heavily planted and established. Maybe 4-5 of them.
I'd do a small colony of shrimp! The Neocaridina family is pretty easy, although they do breed, but you could easily sell them to a LFS if you wanted. So shrimp and a snail of some sort? That's be cool and plenty of fertilizer for your plants that way as well.
5 gallon is still just too small for a school of any fish just because they do need room to swim around, wouldn't be fair to cramp them in a small space, even if it could handle their bio-load.
Leopards: 1:4 Hawkeye, Luna, Astrael, Dorian, Cullen