Deep down, any of these two consoles can become regular old computers. I've seen both machines running Linux, and from there, anything is possible.
I don't think it will be a bigger issue than with any other game. I mean, hell, people have been cheating hard core in Day of Defeat, and Counter-Strike for YEARS and it's still an over populated game.
MK will be fine, online play is going to rock.

well if people cheat on mk then they are shit players....i will be at the top of the xbox ranks without cheating but if any1 does cheat sey like u have points and the most is 100 and some1 has 1000 then i will send letters to boon and complain undistarbingly. so if a cheater comes in my rooom they will get the boot no questions asked....oh almost forgot......how will we play if some1 has a laggy server i mean it will be awful....'pukes while thinking about it'

You don't need a Gameshark or Action Replay to cheat in Socom2, there just glitches people take adavnatage of, and as of now, they've all been taken care of with the new patch. Gameshark and Action Replay don't work online, that's something creators do first when making online games, make sure that cheating with Gameshark can't happen. As for cheating online with PS2 in Deception, how? Getting inside the death trap so no one can hit you? It won't be possible to glitch on either version, and the only thing to worry about is lag.