Sounds like you've got a very specific role in mind for this "professional." I recall you saying it's something required by the club or group you belong to. It isn't really what people (or apparently the agencies) think of as a DM role.
If it were me in this role--whatever we want to call it--I'd write myself a big, fat waiver for the 10 divers to sign.
Maybe. But, when you go out on a recreational charter boat, do you vet the boat and crew and the boat's safety equipment and do a dive safety plan yourself? Or do you assume someone on the boat has done that? If so, who?