I don't think anyone's suggesting he's being waterboarded. There is definitely a distinction between torture and interrogation.
He doesnt need to be interrogated. He is exposing an international fraud. If he is what he says he is, all he has to do is say Hi and the rest will follow.
I'd have thought a few civilized chats over dinner and some vodka would be the best way to handle something like this.
Snowden has literally nothing to lose so whats your point?