The US has experimented with surveillance and suicide drones since about, oh, the 1950s? It's certainly possible, especially when running a large-scale exercise which would require drone surveillance and also drones engaging the AA defenses.
However, I don't think that Air Force intelligence would spend so much time feeding the UFO rumour mill simply for the sake of deflecting questions about drone technology. It likely accounts for some sightings, certainly, but not the overall military interest in the phenomena.