User blog comment:IamJakuhoRaikoben/Chapter 334: Sin and Sacrifice, Review./@comment-5201137-20130608072239/@comment-7418318-20130610105546

So far we only know that Zeref used it to either create monsters, or give live to inanimate objects (Hades created "demons" our of rubble), but that doesn't mean it can't be used for other things too.

If the body is restored, he might be able to give that body life, though that doesn't guarantee it will be the same Gray (Meredy's magic might be helpfull in this matter).

Or that live-giving magic might be used to cheat around the R-Systems limitations (needing a sacrifical body).

That being said, while it might be possible I too think it's very unlikely that Zeref will save Gray's life or revive him. Even if he is close enough and able to, why would he want to?

He certainly didn't try to revive Zancrow, despite feeling sad and guilty about killing him.