I just looked up the term "GameGuard", apparently this is some proprietary rootkit (!) to provide anti-cheat functionality on a single operating system. The Free Software game MegaGlest does not use, incorporate or support this software.
But I will respond more generally, since you seem to be referring to cheating / anti-cheating. Much of this will not work on a real network game. But no doubt, there are ways to cheat and there will always be. A lot of counter measures used to be in place but they also slowed down the game to a point where it became to slow to be properly playable. So it's always about finding a good middle path.
