Mark,
I frame for 3 professional photographers and they all dry mount their photos. I framed for 5 photographers at my old location and they all dry mounted their photos. The photographers down here on the Emerald Coast are getting big bucks for their photos and wedding shoots, I am talking BIG bucks and they all order their photos already mounted from the labs so I have little input in how they get them mounted.
When anything is hinge mounted, photos, prints, or posters, they will be influenced by the environment of their surroundings. If they are hung in a very humid area of the country they will tend to absorb moisture out of the surrounding air mass and this could lead to waviness and buckling of the images. If you are in a dry area of the country like the desert SW, you may not experience such conditions.
My biggest gripe isn't in how these photos are mounted but how I have to handle them when adding mats, glass, and frames. I usually have to either drymount the backed photo onto another backing or inlay them into another backing so they remain centered in the mat opening. Luckily, many of them are framed without mats as is the case with wedding portraits but, without enough extra mounting board bordering the photo, it makes it difficult to place them into a matted frame package without going to extra work to remount the mount onto foamcore or backing board to keep them centered.
Framerguy