It has been my experience up here in Norhtern CA that the club or group that rents the track takes responsibility for establishing their own track rules regarding acceptable condition of cars on track, roll protection, driving behaviors, etc., as long as the track agrees. 

The "advanced" run groups (which I normally would run with) have open passing...which is indeed VERY spirited HPDE   However, since my car is new and I wanted a less streessful track day   I ran with the intermediate run group this time...which has mandatory point-by rules for passing.

Porsches with the hoops (Boxsters) and recent cabs with pop-ups have been acceptable at Thunderhill, Infineon (Sears Point) and Laguna Seca for the past few years, as long as you are running with one of the Track Clubs that has their "agreements" in place with that track. 

However, I agree with you that if a lawsuit were filed, even with signed waivers, negligence would still be considered an issue with the courts.