Sounds very plausible. I think many would agree there are no aliens piloting these craft, and that it isn't that hard to believe there are some groups that the government has either acquired or formed that can make extraordinary craft.

Much of the critique of this idea stems from the idea that our government is incompetent in everything that they do. Even that image of incompetence is something that is potentially very valuable in order to give other nations the false sense that there is no way such an incompetent organization could produce X or Y.