That mostly just means that your mod zips can't directly contain Soldak textures, models, sounds, etc. You don't really want to do this anyways since it would uselessly make your mod a lot bigger.
You can freely reference any of the assets already in the game. For example, placing textures and objects that we created is perfectly fine. Making a new model file that references model data and sounds that already exist is also perfectly fine. Most normal modding will be perfectly fine.
I hope this makes sense.
BTW, I really dislike that we have to have any legalese crap in our EULAs, but it's kind of fact of life these days in the US at least. I wouldn't worry too much about it. We love mods and would never get upset unless you were really abusing the game in some way.
Depths of Peril, Kivi's Underworld, Din's Curse, Drox Operative, & Zombasite