In my opinion, even sleeping people get full Will saves, because the subconscious is a powerful thing, and remains vigilant even when a person is asleep or in a coma. (Not a rule-based answer, but my own personal thoughts.) To my knowledge, the RAW do not drop Will saves for sleeping people, so the Will saves remain as normal.
And in regards to the whole repeated use of a helm of opposite alignment scenario, that sounds a lot like metagaming to me, because that's just playing the odds and the game mechanics instead of roleplaying. (Who would do that kind of thing in-game if they didn't have knowledge of the rules? No one would, in my opinion.) I wouldn't like it if the PCs did that, and that kind of gaming is the reason why I have the following rule in my games:
"Anything you can do, I can do later..."
My players know that if they do not control themselves and they cheese the rules, then they have to deal with the same kind of thing happening to them in the future. Yeah, you get your one moment in the sun, and then it's likely to happen to you. So, if the PCs want their characters in that situation to make a saving throw only once, they'll only use the helmet on their target once. If they want to metagame, the next time they are captured by a bad guy, they'll get the multiple helmet treatment, too, but with something more appropriate to the story or character's situation.
Sorry, but metagaming like that is a pet peeve of mine, as I feel it shows no respect for the roleplaying aspect of the game. My apologies if any would consider my comments above to be inappropriate.
With Regards,
Flynn