I have been to dojo where everyone says os or osu. Quite honestly, I believe that this is common in Japanese dojo rather than Okinawan dojo.
I attended a seminar at a Japanese dojo taught by an Okinawan sensei. At the end of the session, the sensei thanked and said many nice things about the students. They had a dissatisfied look on their faces. The sensei said some more nice things. Still they looked unhappy.
Finally the sensei, looking a bit embarassed, said "os."
Everyone applauded and cheered.
Respectfully,
Charles C. Goodin
