An upcoming marijuana comedy series is fetching the help of Snoop Dogg. The “Gin and Juice” rapper is set to executive produce and perform the theme song for a new MTV show called “Mary + Jane,” according to The Hollywood Reporter. The hip-hop icon will also guest star at some point in the first season of the show, though network execs say he won’t play himself. “You don’t know when he’s going to appear,” executive producer Deborah Kaplan said. “You have to watch all the way to an end to see him.” The new series centers on a pair of millennial girls who lead an all-female pot delivery service in…