In a colloquial sense, coming back from the dead means being revived after your heart stops. A head shot would have made the point moot. When and where Kincaid chose to take his shot, and how it turned out, was probably as much to do with Ivy as Uriel. How Kincaid chose to act made it certain that Mab would be in a position to retrieve Harry after the shot, and that the body would go more or less into stasis until she could pick him up. However, once the brain dies, you're ded, dead. Which is how Corpsetaker got locked out.
My head canon is that neither Harry or Corpsetaker were ghosts. I only say this because both were capable of moving back into a body if one was available. We see this when Butters spirit is left outside his body after being forced out by Corpsetaker. On the other hand Sir Stuart doesn't appear to have this option. My internal canon says that Corpsetaker and Kimmler figured out how to encapsulate whatever it is that makes them human and detach it from the body, much as Uriel does to Harry. This in my canon is how they body jump. And if we assume that whoever gets dispossessed is still human, like Luccio, then they encapsulate the soul as well. So Corpsetaker could take a ride on a train.
I assume that ghosts are souls, but that they couldn't move on, and in staying here they lose their individuality. However the dead fish in that thought is that it makes Corpsetaker a soul eater.