http://forums.eyesonff.com/showthread.php?t=17635
Q) My friend's, brother's, mother's, cousin's, father's, former roommate said that he was able to get Zack as a playable character without using any cheats. Is this true?
A) There is nothing that could be further from the truth; well, not much anyway. It is not possible by any regular ingame means to get Zack as a playable character.