I completely agree Kevin. Properly glued, like you said, is the key. If properly glued...I see it as an additional laminated layer. I would sure take pains to make sure it has close to 100% contact,( on fingerblock...it would be easy to have loose fillets here and there). But if the parquet was installed with the right adhesive, trowell tooth size, and rolled...it should be part of,and additional to the subfloor.
A while back Dennis answered a post on the same subject,(cant find it), but he insisted under ANY conditions the parquet needs to be removed, due to fillets splitting, and making noise under the new hardwood. Hey Dennis! If your out there chime in...I still think that's upselling the job..if it's glued down tight