Would it be fine using screenshots of the TFU downloadable content Sion for a Sion reskin? The screenshots which would be used are from a gaming website, not the actual files. Because it's from the downloadable content, it's not actually really from the game at all, more like from a mod, so I don't know if that would count as porting either.
Personally I'd say it wasn't porting, especially given there is still a fair amount of work still to be done...
For example;
Q: What about borrowing stuff from other games? They don't have read-mes.
A: You have to be careful what kind of things you borrow from other games. Porting models or maps is definitely a no-no, but if you borrow sounds or textures that's usually okay. You must credit them, however. Including them and not explaining where they came from is unacceptable. (found here;
http://knightsoftheoldrepublic.filefront.com/info/Plagiarism_Policy)
As for SW:K rules; 7. Mods containing assets (models, textures, sounds, etc.) ported from another game are prohibited
It is against Lucasarts policy to port assets from one game to another. Holowan Laboratories does not condone porting of this nature, and moderators will close or delete any thread or posts discussing such mods, even if it is for your own personal use. The exception to this is if the asset in question is present in both KOTOR and TSL. Modders may create from scratch mods that resemble assets from another game.
Your's is a grey area, I think it's fine, I'm sure D3 et al will be able to confirm forum policy here. Basically the porting policy in the main is to stop porting assets from KotOR to TSL. I think taking screenshots and using them, from downloadable content to make a screen is definatly not porting as it still involves a hell of a lot fo work still. My 2 cents hope that helps.