If it's a maintenence zap like the DCX3000, just get the cells as close to .6 each as you can. If you go below this even zapping will not save all of them. Hit them with like 50 - 60 and then cycle them after the zapp. Seems Ni-Mh don't responde as well to zapping as Ni-Cd.
Good question, I'm usually more worried about them going under .6v. If you bring them down then zap em it seems to give it some improvement. Not as much as you see on the Ni-Cd's. I wouldn't be concerned if your meter shows them rising before zap.
Now as we have a zapper thread I just might ask a question: How large capacitances or how long zap durations are used in the most common devices? The starting tension seems to be between 30-80V usually.
i use the dcx3000 and i zap my cells after the bulbs have gone out on my equalizing tray. i was pitting next to pat t (one of the integy drivers), and he told me to discharge your cells completely. the more charge left in the cell, the less effective the zap will be. you can even zap prior to charging w/o any ill effects.