I'm in NJ so as long as it's 30 years or older there's no emissions required. If you're in a state that doesn't allow registration of kei trucks then there are companies that make it pretty straightforward to get them titled and registered in states that have very lax laws like Montana.

Not going to say it's right, but for a vehicle that is occassionally used to drive between your home and the hardware store, I'm sure that a ton of these types of vehicles are just not registered. Even if you get caught without registration, the inconvenience is relatively minor (when compared to a daily-driver not being registered)