They won't be able to find out either. :) They would have to call all 50 state DMV's. And even then you could still find yourself stopped by a LEO and given a ticket. There are times when the DMV and the local LEO are at odds about such things. The DMV isn't even sure about the swivel wheel type trailers. It would just depend on who you talked to. Fr'instance you might talk to 2 different people on 2 different days and get 2 different answers. That has been my experience.
I towed a SmartTrailer through and in several states that don't allow double towing and was never stopped or even looked at twice, but YMMV. I just figured it was easier to seek forgiveness than permission. :)