I think the bearings are lubricated by the rear end grease splashing on them.
Not in the Imperial. There is an inner seal that isolates the bearings from the axle housing. The bearings must be lubricated before installation.
It appeared that someone in previous years had had the axles out, carefully cleaned the bearings, and reinstalled, very likely working under the mistaken idea that they were lubricated by the rear end lube.