The range I'm a member with has two separate ranges, both indoors; one for members and one for the general public with a RO in both. They allow practicing from holster draw, and I'm grateful for that. I practice every time I visit, and I've seen many others doing the same. The golden rules for holster-draw-firing are, do not do so any faster than you can safely control the firearm (of course), keep boogerhook off bangswitch until target is acquired (of course!) and DO NOT sweep anyone with your muzzle (of course!!!).
Regarding shoulder rigs, something someone might find useful:
9 times out of 10 I'll be carrying IWB, but i do carry my 629 in an old-school safariland shoulder holster when i carry it. Unlike most folks i've ever seen with shoulder holsters, I wear the gun on my dominant side, (I'm a righty, but carry it where most lefties would). I've practiced with empty gun (and later on live-fire) and discovered it's safer and faster for me that way. Next part is hard to describe with words vs video, but basically when drawing, I pull the gun straight out of and away from the holster, not up, and as I'm bringing it to target I twist it from 'upside down' to right-side up (without finger on trigger of course), and the result is the muzzle goes from holster, to target in a straight line, from resting in holster, to pointing at the ground in a straight line, to target. Basically from me to being pointed down range instantly. Unfortunately this can't be done with a horizontal shoulder rig, but easily done with a vertical shoulder rig.
(photos to show holster I'm writing about, I've had this holster since I was a little boy, used to use it for my cap gun
The draw I've described is possible because beneath the 'belt flap' seen in the photo, where the lug under the barrel would be, isn't closed, but holds the gun with spring-retention, allowing gun to be pulled straight out instead of having to be pulled up and out)