A girl (or Guy) who is dating (or just screwing) someone associated with the music business (DJ, Artist, Manager, Club Owner, etc) to get free access to shows. Similar to a Gold Digger, but based on concert access, not just money.
H: Did you see that hot chick with Steve?
N: Yeah, but she's just a show digger, she don't really like him.
H: Hmm, Maybe I can hit that next concert...