As its already been mentioned, crypto can be contracted from drinking water soiled from feces. Rodents kept in unsanitary conditions may be at higher risk. Any animal can contract it. This is why it's so important to get your rodents from a reputable source (or breed them yourself). Interestingly, freezing the rodents does NOT necessarily kill the virus/bacterium. If the rodent already has the virus, then its there no matter what. So the guy telling you this was not telling you the whole truth.
There is no need to worry though. This virus is not common in snakes and if you are familiar with and comfortable with your rodent supply source (which you would be if you breed them yourself), this should never be an issue. Thousands of people feed many thousands of snakes live prey and do not have any issues. I think your snakes will be just fine!![]()