Is Herschel different from other people? And, if so, how is he different? He died and didn't turn into a zombie. He was able to be revived.
OK folks, time for biology 101. Just because you stop breathing does not mean that you are dead. You are not officially dead until the brain officially checks out. You can be revived if the heart stops if it is within a reasonable amount of time.
If you recall back in Season 1 at the CDC, Jenner explains how the process works. The initial infection from the bite will kill you. You are not officially dead until all neural activity ceases. He shows this on the computer. Once the brain has stopped functioning, it takes a little while for the "virus" to restart some sort of minimal neural activity.
As long as the brain is functional, the reanimation process will not activate.