In the end, it's the owners responsibility to be driving a legal (DOT Approved) vehicle.
That’s just what we’re discovering a DOT approved vehicle is a myth. It’s up to the manufacturer to determine whether it’s “safe”. Now if it’s not the manufacturer could be liable of all sorts of things that could bankrupt Bill Gates.
Now I’ve been holding out some, I’ve studied this extensively, I don’t claim to know all and am always looking to learn more. Except a very short list of items there are no “approvals” for any thing and those that are it’s a matter of filling out the appropriate paper work and require no testing. Even wheels only require a weight rating to be approved, there are tests for those for a DOT stamp but only a weight rating is required, and that’s proven with the number of poorly cast Chinese wheels that have been sold here for decades with just a weight rating.
Which brings up another related subject that really is federal law. If your vehicle is road legal in your home registered state it’s legal anywhere in the country no matter what the local mounty says, if he/she causes you grief about your modified vehicle that is not related to a traffic violation he is in direct violation of federal law.