Depends on the hubs.

Back in the olden days, hubs didn't have any kind of seals and I used to open up mine and to clean and re-grease at least a couple of times a year. Most of the fancier wheels today have sealed cartridge bearings that are all but maintenance free. Virtually all cup and cone bearings have some kind of sealed mechanism. There are different sealed mechanisms and some are sealed better than others but all of them are MUCH better than the old hubs that I grew up with. I pretty much don't do any hub maintenance today unless they need a cone adjustment or if they start sounding dry. A lot of riders still overhaul their cup and cone hubs annually.

I would expect an additional bike shop service charge for overhauling hubs during a typical tune up.