I really don't think they smell any more or less than other animals. Fresh poop stinks especially when it's smeared all over a wheel.
Hedgehogs themselves have no body odor so they aren't like ferrets in that respect. As for hedgehog poop vs ferret poop, well I'll take my 30 hedgehogs poop over our 6 ferrets poop any day.
That being said, there do seem to be a lot of people, parents in particular, that complain about hedgehog smell. If someone is really highly sensitive to smells then I would say no to a hedgehog. Even with daily cage and wheel cleaning, there is overnight when they are up and active and pooping, that there will be some smell. It all depends on his sensitivity.