I built some DT Onyx/Velocity Synergy/WS DB wheels back in 2005, after getting an excellent deal on hubs. At the time, DT Hugi were very popular (no longer made, replaced by current 240/340 series hubs). The Onyx were DT's "cheap" hubs. I built 3 wheels for use on 2 bikes: 36h disc rear, 36h disc front, 32h rim front. I used them for 6,000 miles, nearly all on pavement, and never had a problem.
I recall discovering a loose locknut (minor issue) on the rear hub at the end of this period, when I cleaned and regreased bearings. The rear hub has 1/4"/ 6mm ball bearings on the drive side, and a cartridge bearing on the non-drive side. All the front Onyx hubs use pressed-in cartridge bearings.
So, in my experience the DT Onyx were good hubs, suitable for touring duty.
A 36h Shimano XT hub may have a little advantage longevity-wise, built the same way with same rim/spokes. An offset-drilled rim like the Velocity Synergy would help even more, since it will take about half the dish out of a std 135mm XT wheel.