They can be legal if they are DOT stamped by the manufacturer having met the various standards and have not been modified in any way.
No DOT stamp or "Modified" after the fact, not legal for Highway use.
You can get away with it.
However if you were to be involved in an accident you just might find that your insurance company could deny your policy leaving you hanging in the wind even if you are not otherwise liable.
A DOT stamp is nothing more than an company stating they meet certain requirments. I have yet to see anything in writing stating they are not legal though.
Yes, if an accident was caused directly from not maintaining your wheels (not checking the torque of the bolts) and a tire came off at highway speeds and caused an accident and killed somebody, you would be liable. Just the same if you willingly drove your vehicle with screwed up steering parts. However, just by having them doesn't make you liable.
The only thing I have actually heard regarding run ins with the law is a few cases in California where it was brought up, but never stuck in court.
Also, pneumatic beadlocks, and two piece wheel beadlocks such as Hutchinson or Hummer H1 don't fall into the above catagorys either. They are %100 percent no questions asked legal.
Either way, we are getting off topic as the OP does not require their use. Pneumatic beadlocks are nice however for expedition purposes if you are in the middle of nowhere and you need to keep moving on a flat because there is still an inner tube that holds air.