Back in the late 1970's I worked Daytona International Speedway. I would be very surprised if it's much different today. During major races they had a fully equipped trauma emergency room, filled with doctors and orthopods and Neurologists and the like, right in the infield.
When the company couldn't spare back-up units, we would jury rig our own private vans to transport to the "hospital"! The track was broken up, one "unit" to each of maybe 10 sections.
As paramedics we were instructed to scoop and go. Period. Under no circumstances was a helmet to be budged -- they were sawed off after extensive stabilization in the ER. Of course, the ABCs but not much more, and nothing more complicated than sweep, chin pulls, pressure over bleeding and very quick immobilization and Boogie!
Racers today are even better "armored" so their exoskeleton keeps everything pretty much pre-splinted for you.
But I'd make some serious inquiry. When I did it, I was disappointed in the work, the view of the race was pretty limited, but I loved the infield life!
Small tracks usually contract with local services for Stand-by ambulances. They don't want anyone to have to wait around. Some smaller Raceways WILL have volunteer EMTs stand by maybe for a free hot dog or two. You gotta ask around.