When I had DL status (and VA/DL were partners), I was able to get on an earlier VA flight after arrival to AU on more than one occasion. They saw my DL Platinum status and treated me as a VA Platinum (which is VA top status).
Not sure if things are still the same (these experiences were 3-5 years ago, and a LOT has changed). But I definitely think if you hold UA status you have a very good chance at getting on an earlier VA flight. As you say, the frequency on this route is very high, usually getting an open seat is reasonably easy. Depends on the day of course