[Perfectlap]

no the broomstick test is only on the track and in a convertible. I don't think I have ever heard of a car rolling over on an autocross. Most of the accidents involve someone not braking and ending up going into the crowd, fence, etc.
One year one of my clubs who have very open courses and not these mickey mouse courses where you aren't ever going straight for more than 30 feet, had it's President wreck his car crashing into a light pole in the Stadium lot.
however difficult, It's definitely possible to flip a Boxster at a low speed event like an autocross if the surface has undulations, and ruts/potholes etc.