Dr J Allen Hynek reportedly believed similarly but may not have put it quite so starkly. Hynek had more and closer experiences with such things in his government jobs. How much is not clear.
I haven't talked to either one face to face. Time will tell.
I think they believed that the phenomena as a whole may represent a number of different ‘things’.
It doesn’t strike me that Vallee believed it was all ‘evil spiritual entities’ if he would say, “I’ll be disappointed if UFOs turn out to be only spacecraft from outer space.”
I think he was interested in how study and attempting to understand all of this might inform our as yet paltry grasp of the real natures of time and space.