After five years of racing and worrying if my insurance (BCBS) would cover a track accident, I found out last summer. I'm happy :) to report that out of nearly $50K worth of bills, I'm out less than $3K, and some of it will probably be picked up by CCS's supplemental insurance.
That being said, I have been told that some employers plans, including BCBS, have specific exclusions for motorsports. I've read the fine print on my last few policies (I change jobs a lot!) and have yet to see any of these exclusions, but I suppose they are out there.
As a side note, State Farm would not sell me disability insurance (income), but did sell me an affordable mortgage disability policy to cover the house in case I was laid up for a while.