Is NSZombiesEnabled supported when debugging applications built with a target of the iPhone SDK 3.x?
Also if it is supported, is there anywhere I can get a list of the possible levels supported?
Yes, it is supported for both device and simulator.
It's "NSZombieEnabled" though (not Zombies). You set it by right-clicking on the executable and selecting the General then Environments section - set the value to "YES". If you want to disable it (and you do for any production build) uncheck the variable.