BlueCrayfish.com

I doubt that snails are carriers of the disease, but I am honestly not sure... I would advise you to hold off until we have a concrete answer. I'll do some research and asking around. Otherwise, just continue to feed things that you know will be safe.

A quick search pulled up this little article: http://www.crustaforum.com/board/showthread.php?377-Crayfish-Plague which says:

The spores do sit on everything within the tank, however, they register even before forming a cyst whether the potential host is really a crayfish. [Shrimp] definitely carry the illness!

Since it says that the spores of the disease can sit on everything, I would advise you not to add ANYTHING from a native stream or anything of that sort. I'm sure the snails would be great food for your critters, but it's simply not worth the risk in this case.

However, you can purchase snails from someone/somewhere that you know have not been housed in a tank or same environment as North American crays and I would think that's okay. But it is very good of you to ask these types of questions BEFORE adding things to your tank rather than later. You're a good crawdaddy!

Yeah it would be awesome to have free food, but it's definitely better to be safe!

An idea for you to do, if possible, is set up a tank for breeding your snails. I don't know about most snails, but I know my ramshorns breed like CRAZY. It's like the easiest thing ever to breed them and my crays love them as a snack. So maybe get you a couple of those asian snails you mentioned, set up a tank for breeding them, and then you have a nice self-replenishing food supply. That's up to you though!