At the end of the day it is each to their own, I prefer sideways because that's what I've been brought up with through my mates but I can understand it is not for everyone. Brunty is nothing in crowdedness compared to some of the track events I've done in the past and those have had involved many drift sessions.
I don't recall the organisers ever specifying no drifting, but I think it would be potentially very dangerous especially on the corner after the straight where there can be a few cars braking heavily and heading for the same corner at once. On a couple of occasions I've found it challenging enough getting round without a lairy power slide happening in front! (I'd love it as a passenger, though!)
There is also a rally course where punters pay for laps that has plenty of broadside action and donuts. Maybe a drift experience could be included in future events? Andy?