"Not protected from disclosure to law enforcement" is still better than "entered into the public record by default" as a result of being offered as evidence in a civil trial.
No. If I took you to arbitration and think you acted illegally, I can send the case documents to law enforcement. Most people don't do this, because it's a hassle. But if you pissed me off or were morally offensive, hell yes I'm doing it. After that, yes, they need to execute searches to follow up on the information.
Only if the terms of arbitration allow you to share said documents.
An NDA cannot stop you from reporting criminal conduct. You can be sued by the criminal for doing so, but this is America, you can be sued for anything by anyone. It doesn't mean that they'll win (And will look a hell of a lot like witness intimidation in their criminal trial.)