Title says it all. Aggro-Animal-Zeds would be a true survival tester.
Flocks of undead crows/birds would be a true nightmare, or even a single Zed-bird would be utterly surprising to any nearby person whether they're "camping" or enroute.
Packs of undead wolves, bears would pose a huge threat to camps and locked doors because they'd be like the L4D Tanks and can take tons of gunfire.
I dunno about undead-fish, but it would sure deter most people from swiming in any kind of water; definitely requiring a boat just to get to Prison Island xD
Undead Dogs, Cats, Elk. The list can go on and on. It would certainly make finding companion Animals and lving animals for hunting that much more scarce.
All in all, if it was good for the Resident Evil series, I think it can work in DayZ SA.
*(Yes, this is the identical posting I made in the forums. Sorry about listing the Experimental-game version, I didn't know what to put.)*