I don't want to throw in here with a "so and so that I know said" type reply but I think it will hopefully shed some light on the matter. Granted this is state specific and I do not have black and white textual evidence to back it up.
My father has sold commercial and light truck tires for over 30 years. He has managed two stores, our own family's and one of the locations of the company that bought us out. Anyway, I asked this question of him a few years ago. To his knowledge, beadlocks fall in with the "mutli-piece wheel" design group here in PA, even though we all know that they are two completely different things. Its a bunch of beaurcratic a**hats in Harrisburg who would rather make large sweeping legislation that covers everything, than get technical and really regulate the things that need regulated. Those laws were created probably before beadlocks were even invented or popular, but they're illegalized by the law just the same.
The crazy thing is, if you own a truck that is old enough to have come with multi-piece wheels, you can still endanger my father's employees and anyone on the highway by using them today as they are OE. I've seen one fail in a safety cage firsthand, its amazing what kind of destruction they're capable of.
As I said, I have no proof that this is infact or not infact the actual law, so dispute or agree with me as you will.
"Hello people, would you like me to murder you now? I'm an offroad enthusiast."
"His station wagon is more Jeep than your topless minivan."