winston89, while a work visa allows him to legally work in the US, he would still need the approval of Actors Equity to be cast in a Broadway production.
I don't know for a fact that Creel was the tit-for-tat trade that was used with British Equity, but he is either in Poppins on Broadway because (a) Equity considers him an "internationally recognized star" (that's how Michael Crawford was hired for DOTV) which allows him to be cast without giving a West End role to an American actor in return or (b) he was involved with a deal with British Equity to allow an American to perform on the West End.
All that means is that if your facts are right about it not being a trade, Equity considered him a "star."
If the audience could do better, they'd be up here on stage and I'd be out there watching them. - Ethel Merman