I wouldn't use it for someone seriously, but I like the name a bit it itself.
I like the nn possibilities as well; Zellie is way cute.
I'd probably just use
Grey for short though.
I have a place in one of my stories named Giszeda as a take off of this name. The place is cold, frozen and under the rule of a tyrant so I figured "grey" and "battle" were great ways to describe it.