MikeFerrara, empty your message box. I'd like an author name for Law and the Dive Pro or an IBSN, thanks.
I've been researching the insurance issue with this exact question in mind.
Technically, the liability would only lie on you if you are diving with a less experienced "buddy" and not in a chartered group (not you in charge or working). But then again, as the more experienced diver, even w/o the DM cert, you would be quite a bit more responsible for issues on a dive.
The way it was explained to me yesterday was this:
If you go on a dive trip, like on a cruise ship or charter, if they do not request to know that you are a DM and have their own, you are supposed to be released from liability because you are not the person required to meet the requirements for reasonable expected care. However, in the event of a dive emergency, as a DM you can make yourself liable for a failure to act. This would apply for ANY certification that requires Emergency Response/First Aid as part of it's core/prerequisites.
It makes sense when you look at it that way. On the other hand, I have heard of some dive centers requesting you present your highest cert level so they can become familiar with who in a charter group has emergency training.