1. This guy should be stripped of his license. I remember reading this article
online where an elder man was being fitted for a hearing aid and the audiologist failed to use a dam of any sort. Needless to say, the silicon actually punctured his ear drum and required surgery to be removed. I can't imagine why anyone wouldn't use a dam. You can't possibly expect to get an accurate impression of the canal if you can't fill it 100% and without an ottoblock, doing so doesn't seem possible without causing injury.
2. With my experience, I've determined an open mouth impression is almost crucial to a good fit. At least for me. I use my monitors at work where I perform manual labor and I find that when lifting heavy objects, my canals tend to shift and change shape. I often times talk, smile, yawn, etc., and I'm not so sure my seal would be near as good without taking an open mouth impression. Actually, next set of monitors I get, I plan to go a little further, using the bite block I provide (1.5"), but this time flexing my ears to their fullest.
I would definitely find another audiologist and if they don't put a dam in your canal, I would walk the hell out. Secondly, definitely get an open mouth impression. Tell them "because you said so. now shut the hell up." I would certainly hate to lose my seal every time I so much as open my mouth too far.