Question: Mothership Zeta DLC

[Brakkyn]

I've seen older posts on this before and scoured the internet for additional information, but I figure the best way to get answers is to ask directly, so I get specific results.

I own the retail version of Fallout 3. Mothership Zeta, the last DLC for the game, is the only one I don't have. The only available place for PC download I have found is Steam. The only way to get it is to own the Steam version of Fallout 3; otherwise, you cannot download any of the DLC's from Steam.

My question: is it possible (or even legal) to simply copy and paste the Mothership Zeta files from the Steam Fallout 3 into the Retail Fallout 3's folder and have it function properly? Would vice versa work?