YES - if you are the driver. Nevada Requires helmets any time you are operating on a road, or trail that is open to plated street legal vehicles. You can find more details at NRS 490
Sometimes. If a community passes an ordnance it is allowed . And then ONLY to get from private property to Public Lands - We are working on a comprehensive listing but you can check the local code for where you are riding here
Ely is one of the best Mountain Towns in America. That they allow for OHV's to park and stay downtown at any of the hotels, or grab a bite to eat is a HUGE bonus.
Elko has one of the most welcoming and broad regulations allowing for you to Ride into and out of the city.
Mesquite like Elko has a very brad ordinace allowing for street use of OHV, they also allow Golf Carts,