My dad was enlisted in the Coast Guard for 20 years. The feeling I got from him was the Coast Guard was given the world in terms of law enforcement power. However, they always try to interact with everyone in everyones best interest. I think yes, they can do whatever they please. However, there is policy, and from what I remember of my dad's stories, that is what got most coasties in trouble. Not violating a law, but violating policy.

That reminds me, I had the "pleasure" of seeing Coasties training on Blackhawk helicopters for their new Jayhawks. Nothing like seeing 2 Blackhawk helicopters at about 100 feet coming across your neighborhood. You heard them, looked, saw, didn't see, didn't hear. Very fast, very low, and very cool.