I believe that does differ from one state to the next. I don't use one, but I'm quite sure that I have seen plates on one before. I'd sure check locally to be sure. If you post what state you are in, there is very likely someone on this group who would know for sure.
It only matters in the state you are licensed in. If it is required in your state then you must license it. In Washington the dolly must be license and titled which is tough to do when there is no paper work with the dolly when it comes in a box.
When we sold them, they came with a Certificate of Origin, just like all the trailers we sell. When a trailer or other new vehicle is sold, DMV takes the Certificate and produces a title. VA, does not require a license plate on a tow dolly. I can bet that most were not titled either. (That is how states and local counties pick up information for taxes purposes.) I would also bet that all tow dollys come with Certificates from the manufacure. What you are supposed to do with it depends on your home state. Our dollys did not even have a place to mount a license plate. I have never seen one with a plate, but I have not been in Washington state.
Thats true Ken but have you ever seen those boxes when they get to Washington? I think out of the 12 we sold only 2 had the certificate and the rest we had to fight to get one from the manufacturer. We had to get an affidavit and jump through all the leagel hoops.