My last trip, the DTD bus was shared with the GF, and the Epcot bus with FW. The MK bus and the MK boat are WL only. It's been a while since I took the AK or DHS bus from WL/VWL, so I don't remember if those are shared or not - I've driven my car the past few times I visited those parks.
The bus stop is right between WL and VWL, so it's not like there's a separate stop or anything - it's just that both buildings use the same bus stop. For the most part, VWL is actually closer to the bus stop than most of WL, although farther from the MK boat (which is why I took the bus to MK most of the time).