The problem with sustained drifting on an autocross course is that it "polishes" the road surface making it more slick and inconsistent for the drivers after you. Depending on the owner of the lot, they might not appreciate their customers slip-sliding around after an event.
The tire rack only ran one season of drifting on their course due to the damage it was doing to the track. That track existed solely for the purpose of testing tires. From what I understand it had to be completely resurfaced after that season, and future autocrosses for everyone were severely limited.
They might not have explained it up front this time but in the future if they state no drifting on course, they have the right to kick you out. Better to loose one person than a whole autocross site. Keep the drifting to
http://www.driftday.com/