Red Faction Guerrilla uses Stardock's GOO system for DRM. So, it should show up in your Impulse account if you have one (same with Majesty 2 and East India Company).
But thats the funny thing... I haven't got around to installing the GG download of Red Faction Guerrilla yet. I did a full HDD wipe and install there should be no trace of the game on my system and yet there it is on the Impulse My Games list.
Edit: Just checked and the two keys are different, Impulse have indeed given me a copy of RF:G free.