I have a personal account with II as well as a DX account. I can exchange my unit with II or DX. You can use one of them, both of them, or neither. You don't need a DX account to exchange in II.
They keep adding new ones so You have to keep checking back and/or watch out for e-mails announcing them
One of my biggest complaints about Diamond is that they do not have enough resorts in the Northern United States or in Canada. So when they bought the inventory of Club Intrawest with several resorts in British Columbia, one in Quebec and one in Ontario (close to where I lived at the time) I was ecstatic. I got sucked in to buying more points on the promise that Embarc resorts would be available to Club members. As usual, it was a Diamond lie and Embarc properties continue to have the restriction to be available only to Embarc members. I think Embarc is now considered a separate "collection". Why did I think this assurance of including Embarc properties would be any more honest than anything that comes out of the mouths of Diamond representatives. None of them even know how to spell "integrity".