I mostly only saw the roof since it was in a line of cars, so maybe it was one of rescue squad ones.@GSTim
The Yamaha dealer closed suddenly. Maybe they have reopened but before I retired it was a mess. Family fighting and all stock was repossessed or reported stolen. Customers property was missing. Lots of civil court issues.
No, they are not able to be registered for road use in NJ. So no, they cannot be used on the road. However, Readington and Raritan Police have one each as does the Flemington-Raritan Rescue Squad, but all of those have somewhat official markings. I think you'd have noticed. And I still don't think they'd be on 202 unless it was extraordinary circumstances (flooding/power out/blizzard/crime scene).
I've seen the Yamaha mechanics rip around behind the business and towards Bensi, but never on the roadway.
Most likely a rogue Hunterdon hayseed just pressing his luck a bit too much.