As far as I understand, as a goblin I can view full Delving upgrade chain, but I'm limited to Delving level 4 and the rest is Dwarf only? The flavor text and requirements seem to imply as much, and it would make sense, just making sure it's intentional.
Also, would I be able to fully upgrade a delving under a dwarf vassal? I currently don't have any uneaten dwarves on hand to test that theory.