I'm at work and didn't read through this whole thread, so if I'm repeating something I apologize...
Another thought is that ferrets also get shots for distemper, and other things. I'd be concerned about what types of shots, medications, etc....the ferrets may have been given and wouldn't trust feeding that to my snake.
And I'll be honest, if I found out I rehomed my pets and they were fed off as prey I would beat the everloving bag out of the person who did that. I would happily take the A&B charge on that one.