Just for clarification on layers, you can't HIDE solid geometry in a PART layer. You can add solid features such as extrudes, holes, merges, etc, to a layer in a part and HIDE that layer. It will not cause the solid geometry to be Hidden. It will however hide stuff like merge sketches and axis and datums from merges that are directly associated to the feature that is on the Hidden layer.
So the analogy I would use it if you HIDE the hole feature layer, the hole is still there and showing, but the axis that is associated to that hole is now hidden. If you want to hide the hole, you can either suppress it (not good for references) OR you can make a part simplified rep and exclude the hole in that rep.
Steve