Brawl does the host thing? Huh, I haven't noticed (usually because it takes me forever to find a game...)
Hackability of a game depends on the firmware/code 'strength' of the game and the wii itself. Servers, not really. But they can be targeted. For goldeneye, the only 'server' you have is the master server, which lists current hosts and redirects players there, etc....not much point in hacking that.