Almost no one does it, but for folks who actually ride their bikes a fair amount they should be checked, cleaned and re-lubed every 3-6 months and completely serviced once a year.. although for some hubs cleaning and lubication is all there is to servicing. If the bike is used in severe conditions, more frequent cleaning and service is required.

More specific to your hubs, White Industry hubs (as well as Rolf wheels which use White Ind hubs) should have their bearing pre-load adjusted after about the first 100 miles or so as some play will typically develop during those initial miles. Same is true of Chris King hubs. After that, the general maintenance approach of checking and cleaning them twice a year and making sure the pre-load is adjusted as part of the process. As you do this you may find that you can go with only a once a year service check, assuming everything seems to remain tight and relatively clean during 6-month intervals. Then again, if you ride in cruddy conditions you'll probably figure out that your hubs may require a monthly cleaning & relube of the rear freewheel engagement mechanism.

Most problems with hubs stem from the loss of preload (bearing creaks & squeaks) or from contamination / lack of lubrication in the rear freewheel mechanism (DT / Star ratchets are particularly vulnerable to this). For folks in dry climates that never ride in the rain, those lubricants in the rear hub will still break-down over time so some periodic cleaning and relubriation is still needed to ensure maximum service life of a the hubs. Mind you, there are always some folks out there who will cite having ridden a bike 50,000 miles without ever servicing their hubs (or replacing chains, etc.); I'm guessing it's kind of like winning the lottery or getting hit by lightning... it happens, but not often.