Note that from the point of view of deterrent it doesn't mater whether cryonics works or not as long as the criminal believes it will.

Suppose you believe that final death is an appropriate punishment for someone's crime. You also believe cryonics has probability p of working, where p is too small for you to sign up for cryonics. Should you allow the prisoner to be frozen?

If cryonics doesn't work, it doesn't make a difference; and if cryonics does, you shouldn't. Thus there is no reason to allow the prisoner to sign up for cryonics.

Notice that this conclusion doesn't depend on the probability of cryonics working, or on how certain you are the prisoner is guilty, for any certainty sufficient to justify him being executed.

That would indeed be interesting, particularly because it would be a good test of how seriously people take cryonics when they're not motivated to deny the possibility of its success (to explain why they don't want to sign up, or why it wouldn't have been any use in saving the life of a loved one, etc.) — we'd see how many of them seemed to be seriously worried about the death row convicts coming back someday.

I think you have just suggested an excellent persuasion tactic. I can't think of a better way to convince people they want something than by having them see it as a privilege that a deplored group don't deserve.