Making things complicated are newer rules that include no floor-length or oversized costumes, but this sort of dress may toe the line since it’s more of a maxi than a full costume.
However, Disney is totally fond of character reminiscent outfits, which means that if you are wearing regular, modern clothing that takes on the look of a Disney character you are good to go in the parks.
At any rate, they are beautiful.
Disney is not a huge fan of adults dressing up like characters at the parks, which means that if you are over the age of 14 and really want to throw on a literal Beauty and the Beast costume, you may be turned away so no one mistakes you for an actual character.