As long as you physically reach GZ* and look (even for a second and then get muggled off) if you don't find it its a DNF.
* Although I still call these DNFs, tree climbs (say) where you see the tree and sometimes cache but don't attempt don't universally go down as DNFs, I was once caching as part of a Meetup group who 'agreed' not to log such a tree climb as DNF, not wanting to break group consensus I didnt!
Not reaching GZ and logging DNF is lazy and bad etiquette.