Just a few of the celebs I've heard have been in attendance at Moz gigs, derived from chatting with other fans and watching Twitter/Solo:
-Chloe Sevigny (MSG 2015)
-Michael Imperioli (Various NYC gigs)
-Quentin Tarantino (Staples Center '13)
-Tony Kanal (various LA gigs)
-Andy Richter (Staples '13/ Sports Arena '14)
-Maya Rudolph (LA Sports Arena 2014)
-Phil Anselmo (NOLA '15)