As for Oahu Diving, they are mostly guided dives and your DM is not only a DM but normally an instructor.
This is an interesting comment I see a lot on scubaboard, especially about HI DM/instructors. Unless I'm taking a course with the person I don't give a rat's ass if they are an instructor, DM, or good old deck hand with no diving experience.
I tip based upon my experience, not the potential experience I could have had based on someone else's qualifications.