I'm a member at Cape Ann Sportsman's Club in Gloucester and I'm 99% sure it's allowed. I've never specifically asked as I usually go there when it's not busy on a Saturday afternoon.
I've done some USPSA/IDPA practice (with my full gear - holster and mag pouches etc) when the club president was there and he never said a word to me. I also see plenty of other members that practice shooting from a holster so I think it's good to go.