Our outdoor range has no regulation against carrying while on the range, and I am nearly always armed while there. The main thing is that you don't handle a holstered firearm during a cease fire or while you are behind the firing line. I'm sure someone will mess that up in the coming months or years.

To my knowledge there isn't a rule against working from the holster, but it seldom happens. On weekends when the range is busy it would be a bit awkward and I can see the RSOs stopping someone from doing so for safety, particularly if the shooter didn't look like they were real proficient. I generally don't practice from the holster while at this range, as I can practice those drills on the range at work or at a place in the desert where I like to shoot.