I think this needs some defining. On many charter boats, divers go in the water and are "guided" by a DM or Dive Guide. Whether the Dive Guide is a DM, or just a good diver with very good knowledge of the dive site, the key reason for them being on the dive, is for them to help make certain that any of the divers that are following them, will not miss out on the cool features of the dive site....but any diver that decides they do not want to follow, will not follow, and that is fine too. For this type of situation, I see no problem with the camera. All divers in this group following, are seen as competent divers.
The other scenario is where new divers really need a DM for their safety on the dive, because they have insufficient training and or experience, to date. As these divers are not competent, the Dive Master must watch them and attempt to proactively prevent major problems, like Low on Air, or panic, or any of the other large range of issues incompetent divers are prone to. As this is very much a by-product of "modularized instruction", where you really can have several divers on a boat that could not safely attempt the dives without a Dive Professional helping them, the Dive Master leading groups like this must know ahead of time that they are not going to be able to play with a camera, as everyone knows this interferes with peripheral awareness. Maybe the head mounted GoPro as DD suggested could be OK, but this assumes that the DM doing this was ignoring what was being shot by the GoPro, and concentrating entirely on the incompetent divers in his group. Not all DM's would be able to make this distinction successfully---many would think they could ignore what they were shooting video of, but as soon as a huge video opportunity presented itself, there would be a strong compulsion to be looking at the spectacle--capturing it on video---and this would mean not looking around every few seconds and scanning the divers to see if all are fine..That would mean missing a great video opportunity ( hard to allow yourself to do), and every time the head turns to look at a diver in the group to make sure they are ok, this ruins the video....This is just hard on someone that likes to get decent video, and so this is going to be hard on the DM ( meaning ability to be a good DM is likely to DECREASE).