Yeah, I would be incredibly pissed if they shut me down for using a cracked EXE on a game I own, but I don't think they give a shit. I have been using a cracked EXE for widescreen in KOTOR and it even lets me start the game through Steam fine still. I think the only time it check file integrity is in multiplayer games/when you verify game cache and when you do the verification thing, it just replaces the file with the one from their servers and you have to choose to do that. If Risen cracked is started with the regular EXE file and not a bat file or something, try clicking the game in Steam. It should work fine and you will get Steam community without having to add it manually/your time played tracked.
That said, Steam NEEDS to actually ban activation limits. That shit is stupid as hell. *Crysis rage*