The reason most beadlock wheels are illegal is because they do not meet DOT specifications. For a wheel to be DOT approved it MUST have a safety bead. The safety bead is what keeps the tire on the wheel when you get a flat... if you've ever watched a tire being mounted on a rim you will know this sound well... when the tire is inflated during the mounting process you hear a loud POP. This pop is the tire seating itself between the safety bead and the outer rim of the wheel. Because beadlock wheels normally do away with the safety bead they are not DOT approved, and if it's not DOT approved it is illegal for use on public roads.
Now if someone were less than 100% honest you could in theory BS your way out of a ticket. I won't promote or condone it (don't do it) but if you get pulled over you can LIE and tell the officer that your wheels in fact have the DOT mandated internal safety bead and that your external bead lock is simply there for additional safety and support required when running lower air pressures off-road.
Jeff @ PLC