I know the police departments are usually aware of them. And that there is a national organization offering training. I'm not sure that means that these neighborhood watch groups are controlled by law enforcement - or that all of them are registered because they have to be registered. I think it's just a cooperative effort. (Or do you have a link otherwise?)
If five guys in my neighborhood decide they want to patrol our neighborhood streets on Friday nights,and they're doing nothing wrong, why would they be arrested? It hasn't come to that yet, has it?