I mean, in 2006 I saw the Roots co-headline (but perform before) Gym Class Heroes (I left before they hit the stage). Come to think of it, a few years prior to that I saw the Roots open for 311. Rap-rock didn't last, who woulda thunk???
Saw Incubus co-headline (but possibly with a shorter set) before Deftones back in like 2000. Crazy thing is I saw them both 15 years later together, in an arena instead of a little theater, and the order had flip flopped.