If OP or anyone else owns HGV Max from the HVC side and purchases a resale HGV deed, that resale HGV deed would have only HGVC access and no HGV Max access, so could not be used for an HVC (old DRI) or Embarc reservation. Similarly, if someone owns HGV Max from the HGVC side and purchases resale HVC points, those points will not be in The Club and will not be able to be used for an HGVC or Embarc reservation.
One interesting thing I've noticed as an HGV Max owner from the HGVC side with resale HVC points, the resort credit portion of the HGV Max Tier benefits bleeds through to the HVC side of things because my two accounts are connected through the unified website. The open season credit does not. I'm not sure about the room upgrade part of things as I only recently got the HVC points, have only made one reservation on that side, and don't have any experience with how the site shows upgrade for tiers. I don't expect that I'll have the room upgrade benefit, though stranger things have happened....