O-ring once bubbled...
It seems that helping with classes would be either covered by the instructor's insurance or at least some type of cheaper rate....I would never be in charge of divers (certified or uncertified)...just assisting with classes under the supervision of an instructor with insurance.
Actually, you could be in charge of divers quite frequently, depending on classes and your instructor. A DM can take OW students on a sightseeing tour on the third OW dive if memory serves, as well as being the only pro in the water on some of the advanced dives. You can also take them aside duing confined water for skills practice.
I would not consider DMing without full insurance.
Phil