"I wonder what will happen the first time someone gets banged up for violated the terms of their release based solely on the polygraph and it is later proved that the polygraph was incorrect."
It will never happen. It's certainly not whats happened here.
The suspect confessed to a violation of parole. That's what the evidence is. If they want to retract the confession, they will probably have to show some reason for it. If this is "I was being whacked over the head with the yellow pages" then the confession will (hopefully) be thrown out. If it's from something that is considered an acceptable interrogation technique, then it's acceptable.
So if you have two suspects in custody, it is usually acceptable to say things like "your mate is busy telling us everything and is going to get a sweet deal" or "you totally done it, we know you done it, confess now and we'll go easier on you" or "if you don't 'fess up, we're going to arrest your mum/nan/child since one of you lot done it". Saying "I know you're lying, I have magic powers/technology" is probably fine too.
As an aside, it's often pretty easy for me to tell if someone is being deceptive. When your safety depends on reading people's intentions it's instinctive, and I'd imagine most LEOs have something similar. Determining exactly what that deception is covering up is a whole other ball game.
I would also suggest that if you're talking to the cops and are guilty you should probably get a lawyer. If you are innocent then you REALLY should get a lawyer before answering. Or decline to assist until they arrest you.