FFH uses the Bloodthirster and some minor demon from Dawn of War, several units from Sid Meier's Pirates!, a treant from Warcraft III, several buildings from Kohan II. you get the idea. Corporations generally don't care much about non-profit fan mods, and it's not worth their time to do anything about it in any case.
If you really want to pursue this line of thinking, consider that the ENTIRE planetfall mod is a trademark and copyright violation to begin with, since it's openly and explicitly based on a commercial game - alpha centaurii - and reuses characters, concepts, unit types, images, names, etc from that.
Also the entire dune wars mod is a violation similarly. Oh, and then there's the star wars mod, of course. And while FFH is kael's original work, many elements within it are not. The Radiant Guard and Sphener units for example, are 3D interpretations of 2D art owned by artists unrelated to the project. Every single leaderhead is copyrighted artwork taken from the internet, sometimes with permission, sometimes not. Likewise with images for scenarios. And then there's all the mp3 music from Arcana in it. And isn't the entire sword and sorcery genre just a big infringement on JRR tolkien anyway ?
Also bear in mind that it's outside of modding plenty, too. Feel free to chase down all the people who cosplay as space marines, or sephiroth, or whatever, for copyright infringement. And go after people who write fanfiction, or create fanart. And it's not even just fans that do it. Corporations rip each other off all the time. Did anyone notice there was a Power fist in Fallout 3? And how many non-starwars games have had lightsabers or some slightly renamed knock off.
Copyright infringement is so ridiculously abundant in every facet of everything, everywhere, that it's generally ignored unless it actually does someone harm, or one company just feels like being a complete prick and alienating their userbase. Distributing free copies of a commercial game for example, can be argued to harm the developer. Distributing one heavily optimised and modded unit from one game, in one specific format for one specific purpose, causes harm to nobody. It doesn't even cause lost sales from people who might have bought dawn of war JUST to rip a space marine model from it, because the unit I've uploaded here is so heavily optimised that a great deal of the original detail is gone. It's polycount is less than a third of what it originally was, the flamethrower is mangled to suit my purposes, and all the other weapons, the helmet, and the original backpack aren't included in the nif..