Yes, you do have to purchase a set of tires for the event from TireRack - at 25% off their advertised price.
To clarify what Neil said, anyone can get the SVRA license, and drive in the skidpad and drag race events. The road course time trials require the driver to have "some" HPDE experience" at a minimum. It's not very definitive. Go to the website. All of this information, as well as a listing of the acceptable tire brands, is there. www.onelapofamerica.com