Well, I think Wildcard has said as much as their assets are essentially free-for-all, though I think it then becomes a question of morality and ethics if one were considering using them in a published game without replacing them - but you’ve stated you intend on doing this. Either way, I believe the answer is yes.
Nowhere, to my knowledge. I don’t think anybody’s gone to the lengths of stripping out specific types of assets for public use, there’s really been no need as people generally mod for ARK and don’t need/want the assets for something else. That said, I believe you’re left with downloading the DevKit yourself to get what you want unless you can convince someone to do it for you and upload them somewhere you can download them.