most will handle a hard nite or 2, its when them hard nites turn in to 4/5/6/7 nites a week that i think the whippet losses it appeal, they just drop condition an are too fast for there own good.........
if i was to buy a dog solely for ferreting however, a whippet would be top of my list
i only go once or twice a week due to work
then depending on the land ye run, a whippet could be an option mate, but if ye think you might do more, or you run ruff ground maybe a whippet based lurcher, best a both worlds