My Dwarfs do eat the Ghost shrimp if they see them, 6 in the tank will usually last a week before I can't find any more. As for snails I do the same thing, get the lfs to dig the pond snails out of the plant tanks or the sump, my pack of 8 gets about 20 a week and they make short work of them. You may be able to supply all your snails to the puffer from your other tank, it would depend on how many puffers you had. Your own snails would be safer because you know they are disease free, and you could keep the snails fed with high nutrition foods to help pass the goodness on to your puffers (you are what you eat)
edit: I haven't found anything that will substitute for snails with the dwarfs, the bigger puffers will eat clams and muscles nicely as well.