Can internal parasites pass from mice to a feeding snake?

Yes, they can. While not all parasites can pass, enough of them can that I would never recommend feeding something that doesn't look healthy to you snake. Snakes are very sensitive to bacteria and parasites, and its usually better to be safe than sorry, especially if this snake is a rescue and isn't in great health to begin with. That said, fuzzy mice and rats can very quickly die if they're not kept in a warm enough environment, so that could be the cause. I would just keep a very close eye on your corn and talk to your vet if anything seems amiss.