Originally Posted by
oldbobcat
.. Those hubs have threaded end nuts, which suggests that even if the bearings are sealed,..... .
Sorry, but the fact that it's a threaded axle and end cap tells you
nothing about the bearing.
If could be a classic cup/cone called "sealed" in the literature, because there's a seal. Or it could be a cartridge bearing, either radial or angular contact. However angular contact cartridge bearings are rare birds in the bike world.
FWIW my old SunTour Superbe Pro hubs had radial bearings with a system that fully resembled a classic cup/cone system. They allowed adjustment for axial play, but wanted zero preload.
So, the real answer for the OP calls for looking past the seal, knowing what's in there, and proceeding accordingly.