[roark fishies]

I wouldn't do the DP with a betta. Or any other fish for that matter. They can be quite aggressive fin nippers. Like kissy said, they are best left to a species only tank. There's always exceptions to every rule like in butters case but I wouldn't risk it.
Also, what about an african dwarf frog? They stay really small but you have to make sure they get their share of food as they are not aggressive eaters. If the other fish always to get to the food before them they could starve.