I just remembered about Steve Martin, and that Stephen Colbert is and he did a nice segment after Glenn died thanking him, Don, and the band for writing "Desperado" as that was the song he first danced to with a girl at a school dance. I think I remember reading on here before too that Conan O'Brien is too, as well as Andy Richter. And sticking with the late night talk show theme I think Jimmy Fallon is. He loves 70s & 80s music and does so many sketches about it, as well as doing the same on SNL.
And Fred Armisen from SNL and "Documentary Now" is and why he came up with the Blue Jean Committee with Bill Hader who just liked the documentary. Not sure about Seth Meyers who was involved with it too when they first did the SNL skit.
But I do think the most celebs I know that are fans are musicians. Did find an article on Entertainment Weekly talking about when Glenn died and saw some actors and celebs tweets were mentioned too like Miles Teller (who was in that great jazz drummer movie "Whiplash"), Fred Willard, Andy Cohen, and Carson Daly.
ETA: Found more on this People Magazine article with Rita Wilson, Larry the Cable Guy, and Hailee Steinfeld (a younger actress I've like in a couple movies, also sings and plays guitar, and met Glenn).