I am not aware of a way to run it against a whole pool, you can either run it against a single device, a device range, a given storage group or a device group. So if you add all of the device in a pool to a group you could run it against the whole pool. But I am not sure how time that would save you.  As for checking, unfortunately not possible either. The only time Enginuity examines a TDEV for zeroed space is when you initiate a reclaim. So you won't know until you try.
Is there a way to run this against a whole pool or even determine which devs to run it against? I'm finding that a number of thick to thin PPME (hostcopy) migrations have occurred in our environment and it appears that under this condition, the target TDEV is fully allocated which is an incredible waste. I have run reclaimation against devices I'm aware of what about the other thousands?  Thoughts.. ? thanks ! 
run zero page reclaim against a whole thin pool?