To clarify a little, the Vader and first six stormtroopers in the Disney Christmas parade are Disney employees and Disney owned suits. The rest of the troopers were from the 501st costuming group. Since they had a little "choreography" in the front (mainly just the pose with the pyrotechnic-rigged blasters), they used Disney employees.
The Vader used in the SWW parades is a Disney employee, too. The stormtroopers seen elsewhere in the parade apart from the large 501st group are Disney's, too, as well as any troopers seen anywhere else in the park during the day. The 501st (and Rebel Legion) costume groups are kept together in the parade. We've done some other events for Disney, such as the "Last Tour to Endor" closing of the Star Tours ride, which allowed us to mingle in the park, the grand opening ceremony for the new Star Tours, and a couple corporate events held in Hollywood Studios. They even called on us to play pirates for the christening of the Disney Dream cruise ship. That was fun, considering my day job was in marketing for a financial institution at the time.
It'll be interesting to see what will happen now that Disney owns LFL. Hopefully more trooping opportunities!
Scott