I'm going to talk about transferring a model from a game which allows its models to be used as a modders resource so I can speak freely and in an understandable fashion.
I am in the process of learning how to transfer Witcher 2 models into my skyrim, which as I understand it you can do after you configure blender to open those files, then you send them through nifscope into a language that skyrim understands and then its just a matter of getting them actually in the game. (I could be wrong at any point here, feel free to correct me, as I have yet to get those damn files to open in blender)
That is not true. The Witcher 2 has a EULA (just like every other game) that you agreed to and within it (I just looked) you agree to "You may not decompile, modify, reverse engineer, disassemble or otherwise reproduce the Software".
So no, you cannot legally transfer the models, and this statement is true for pretty much any game out there.