Is the small hole in the dust cover/cap to inject oil as well?
I've never done that. Oil goes in the center of the hub -- you want the migration to be out the axle ends, so that dirt goes that way. Shimano Deore XT hubs (I have some of these, too; nice) have an open/close oil port on the sides of the hub. There's really no need to inject oil more than one place, I think.