Just booked an itinerary including VA LAX-BNE-PER in PE. I found the routing but called the Diamond line to book because I'm returning from Xian, China and wanted to use GUC on that leg on DL. The agent had no problem getting me seats both transPac and from BNE to PER. I later talked to Virgin because I wanted to see if I could use their "auction" to upgrade to premium on the domestic flight. The VA agent confirmed my seats were selected on both flights, but that I couldn't use the auction since it was a DL ticket.
Not flying for a few weeks, but I'm thinking this will hold since VA sees it on their www site.