Ive tried several plecos in my Piranha tank and all of them came victim to them. Even though I feed them twice a day, beefheart and live feeders, they still hit the plecos. The snails and craws sound like your best bet. Good Luck though.
I put 50 ghost shrimps in my RBP's tank and they seem to be doing well, they are the one eating the left over pellets and dead fish parts. Although I have drift wood in the tank for them to hide in.