The ex-U.S. military planes, yes (not many civil B-52s or SR-71s) are still government property and loaned to the museum.
Others have been loaned by their owners..like the Ex-Tora, Tora, Tora Japanese Kate replica (or is it a Val?…I can never remember:)) and the Indian Gnat. See post #3.

So there are a few potential flyers in that pile?:D