The EGPWS inhibit switch just inhibits the E part of the GPWS system, the remaining modes of the GPWS are still active.
I dont fly the NG but would take a guess that the inhibit removes the terrain data base from the ND which may be why the vert position trend vector is removed?
Some airports have significant close in terrain that may be difficult to map, or the nav solution not accurate enough for the terrain database that can cause false warnings. I operate to two such airports and we are authorised in VMC on finals to select overide.