There's one gym I was at and they refer to all the black belts as master. So you would greet them as master <insert name here>. Is that common anywhere else?
No, in fact it's actually incorrect usage of the term. In BJJ "master" means someone is 7th or 8th degree black and red belt.
Professor from 2nd degree black belt
Master from 7th degree black and red belt
Grandmaster from 9th degree red belt