I manage park hosts (not for USFS though).
NPS pays in some cases, not sure about forest service.
Exact duties will vary widely by park/agency. My agency requires 20 hrs/week for a full-hookup site.
Find out exactly what your duties and expectations are, especially re:other campers. I generally don't recommend backing other people's trailers, for example, and if you do that it's on you, not us. If you don't like cleaning bathrooms, make sure you ask if that's on the park host duties list.
Understand that you will get knocks on the door at 2am for the dumbest shit. If you can't maintain a friendly facade sure those interactions, this job is probably not for you.
Re:rules/law violations. There is a balance you will need to maintain. I don't expect to get a call every time you see a beer bottle or pipe or whatever. But, if I get camper complaints about a giant trashed-out campsite with 85 people and drugs and aggressive dogs and whatnot, and it turns out that you knew about it and didn't say anything because fuck the police, you're packing your shit immediately.
On the flip side, if you treat your campground like your own personal fiefdom and go rampaging off on someone for parking with a wheel slightly on the grass, all your going to do is cause complaints, and you'll be parking your shit.
Thankfully, most hosts are rational humans that can tell the difference between (or don't even bother looking for) little piddly shit and things that can actually affect the safety of well-being of the campers or the park itself. One thing I would ask is that if you DO see something that you need to report, for the love of fuck do it right then and don't wait till morning. Reporting the guy that went ripping through the campground at 2am in his loud-ass truck shooting guns out the window is kinda pointless if you wait till 10am to report it. This is my biggest pet peeve with park hosts.
Its also worth saying that some park hosts are busybodies that LOVE stirring drama with other hosts or park staff. Don't be that guy. Get your hours, and don't worry about if/how someone else is getting theirs.
As you can probably tell from this post, 90% of park host headaches are caused by hosts' interactions with campers and each other. It is a people-forward job. Know that before you go in.