Chris Faraone of the Boston Herald looks at the presence of hip hop on the Vans Warped Tour.  The tour added a hip hop stage in 2004 featuring Atmosphere though rapper appearances go back at least to 1999 when Eminem played 30+ dates on the tour.

Official Site:
Vans Warped Tour

Related ProHipHop Coverage:
Vans: Just a "cool, native southern Californian youth-culture brand"