Really quick question, and I know I asked pretty much the same thing a few days ago about FWE, but can you apply weapon mod kits to weapons added by FOOK?

Not unless there was a patch made for it, which I didn't see in a casual search on the Nexus . WMK simply replaces the default weapons in the game with a version that has the attachments added to them. You're not actually adding the kits as such, the entire weapon is replaced. That just makes it look like you've added the attachments.

There's a current FOOK - WMK CP made by Antistar available http://www.fallout3nexus.com/downloads/file.php?id=4968.

Well there you go, just use the patch FOOK provides. I don't use that mod myself so I wasn't sure if there was one or not. I wouldn't want to play without WMK though.