I have a dwarf blue and a red scarlet in my nano with zoas and both are model citizens, at least until the dwarf blue decided they like the red scarlet's shell better, so I'd go for the other comments about setting up surveillance or closely watching the tank before pulling livestock...

My three biggest fears, in your situation, would be to (1) introduce a predator I don't really want or need who doesn't solve the problem, (2) take out things I do like on a hunch and it doesn't solve the problem, and (3) reduce my CUC only to find out they weren't the problem