The wheel bearings on my 9" (and all that I have seen) is a sealed greased bearing. The
oil in the housing does not come in contact with the wheel bearings.
There is an
oil lip seal that rides on the axle. Too little
oil and it will fail. Too much and it will leak.
I have seen a lot of 3rd members for sale at swap meets, and I have never seen one without the oil fill hole. I'm not saying it is impossible, but it is much more believable that it was missed. I would like to see a picture.