Hi spish,
I've used it in the past, in a 50-50 mix with dolomitic limestone powder dusted over each bird. It seemed to work. I'd only had a very light infestation of mites though. I used it quite liberally in the pen and nestboxes with no ill effects.
I've also used it on cattle and it seemed effective.
Now though I tend to use rotenone. It's quite toxic so I'm fairly cautious, but it's nowhere near as bad as organophosphates and it works (and is allowed under organic systems because it's derived from a root).
I haven't used sulphur dust orally with chickens. I'm not sure how much sulphur they can tolerate or whether the powder is pure. But essentially garlic works as a worm repellent by being high in sulphur, so maybe it's worth an internet search?
cheers
Erica