Oh its absolutely within the realm of possibility, i just cant believe anybody would be crazy enough to do all that work for free and risk being sued by capcom (modding in the case of japanese devs is a matter of tolerance, not support. Once you start making a multiplayer mod you are actively creating competition to their MMO title while using their copyrighted material.) Just Cause runs on a more moddable engine and the guys who made the multiplayer obviously had some kind of support or at least approval from the devs.