I must say I don't see why any professional aviator should have the slightest reservation about reporting a UFO. It is (after all) just that a flying object that he or she could not identify. Now what on earth is wrong with that?
I saw two during my time. Reported both. One was explaned the other was not. So what? Both had ATC implications as after a while one looked as if it suffered a mid air explosion and the other was in a restricted area.