I am not a photo conservator, but I suggest looking at the Photographic Materials Group Wiki entry on Humidification, Drying, and Flattening. The Drying and Pressing Treatment Variations offer specific information about using a dry mount press (both with and without heat) to flatten photos, including (under the Pros and Cons of Variation #2) some cautions about the technique. I’m not sure what type of photographic process you are working with, but the Wiki discusses a few different ones.
Though it does seem that there are some potential negative side effects, if the alternative is for the photographs to be discarded there may be little to lose. One thought would be to flatten them enough that digital copies could be made, if that’s an option for you.
I hope this helps!