A call to the Fremont Street Experience revealed that, so far, there is no official theme, or at least not a named one, for this summer's free entertainment lineup, although they suggested we might like to look at the scheudle and come up with our own name, and we invite our readers to do the same; we'll share any good ones after this answer has run.
In the meantime, here are the current confirmed performers:
May 26 (Sat.) -- Vince Neil –- Mötley Crüe front man -- 3rd Street Stage
June 9 (Sat.) -- Dennis DeYoung: The Music of Styx -- 1st Street Stage
June 22 (Fri.) -- Night Ranger -- 3rd Street Stage
July 7 (Sat.) -- Asia featuring John Payne -- 1st Street Stage
July 21 (Sat.) -- Warramt & Skid Row -- 1st Street Stage
Aug 4 (Sat.) -- Bret Michaels "Get Your Rock on Tour 2012" -- 3rd Street Stage
Aug 18 (Sat.) -- TBD
Sept 3 (Sat.) -- Dee Snider – Singer for Twisted Sister -- 3rd Street Stage