We actually don't know for sure what FF zombies can do yet. With any luck, they're mostly the same as the games have shown (as in, vulnerable to Fire and Holy and maybe can also be killed by healing spells). On the other hand, it would suck if they can also temporarily turn someone into a zombie, as shown in some games, because that would be all kinds of suck.

I'm really not sure which is worse. Zombies are pretty nasty. Even if they can't infect you with a zombie virus, it's still a dead rotting body walking around and probably carrying some nasty germs. Although, generally, they aren't available in near infinite numbers. The Heartless don't have the germs, but they do have the numbers. Both tends to mob... it's probably subjective...