I've flown on VA a couple of times booked from DL.com. No problems at all. Seats I chose were the ones I sat in. I don't recall getting a VA number, but I didn't need it anyhow.

Only "problem" I had was the scanner in Sydney didn't want to scan the boarding pass issued by Delta. They printed a new one on VA paper and I got on the plane. No problems getting MQM credit on any flight.

VA is a fine airline, very happy with the service I received flying them from SYD-DPS, DPS-SYD, and
SYD-LAX