Under normal conditions, Formalin can cause fog. It is a reducing agent that is known to cause "R" typing.

OTOH, it is such a powerful hardener that it retards swell and development and therefore you can lose speed, contrast and lower fog.

It is therefore a tossup as to which you see. Usually, Formalin requires long times to cause fog and speed increases, and that is why it is not used as a means of inducing higher speed through R typing. Usually, Formalin acts over several weeks to months to years, depending on level.

Now, that said, all of this is for gelatin alone.

IDK what your polymer is Bill, nor what the modifications are, and therefore I doubt that anything I say would apply to your conditions due to other reactions that might take place. Formalin is quite reactive and can release a host of byproducts when added to many materials.

EDIT: In an afterthought, I realized that in all the years of research at EK, Fuji and Ilford, no total substitute for gelatin has been found that will allow good crystals to be formed. Therefore, if you have Bill, I believe that it is patentable. You should get some Electron Microscope photos of the emulsion and some speed comparisons with gelatin for this and go for it!