That's right. Shaun Goeppinger's UT2004 mods. The site has several interesting "things" you'll find useful and fun, like DOOM3, Alien, Pikachu, and some other skin mods. Click
the "UNREAL" tab, then click "monsters" and you'll get different mutator skins.
You don't get to use the skin mods (mutators) in KF as easily as you do for Unreal Tournament 2004. Not unless you know coding. But the animations, textures and other files are there for your use.