Agree, the runway will display on the VSD in correct place even with an incorrect QNH set on the altimeter, however if the terrain that is displayed on the VSD is obtained from a data base (the EGPWS data base) and this is relative to the barometer derived aircrafts vertical position, which the EGPWS uses (as stated in Boeing Vol 2), then the terrain should also be depicted on the VSD in the same vertical position in relation to the runway. i.e not displaying the true aircrafts vertical position in relation to the terrain below.
Or is the aircraft symbol on the VSD's altitude in relation to the terrain obtained by some other altitude means that is not subject to miss set QNH??
Thanks for reply's