Yes you can use the darkmatter models with fps creator, AND the skymatter stuff (i think!), it's just renaming the sky textures and placing them into the right places, but as for the models in darkmatter, he
can use the static models... but as for the characters or guns it's hard to get them ready for fpsc. but it is not imposible to rig them.. so i think you're gonna be ok..
it should be easy to rig the static (not guns or character) models for fpsc with the entity creater tool availible on the fpsc website.
i like furry jesus and sódóma just more than anything else..