Sorry if:-
a) I missed your point or
b) I'm looking at the wrong thing.
I just tried a VERY quick run through with the VTape Flanger (just to refresh my memory) and, unless I'm mistaken, the Position is determined by the 'Speed Diff' knob. In my quick test, altering the 'Speed Diff' caused the Position indicator to react and this WAS picked up by host automation AND was played back correctly. I'm using Cubase btw. I wonder if that could be a difference.
Chris