Just signed up and I linked United Club as my FF.
I'm looking at booking flights with Virgin, couple of questions:
1) Is there free luggage through Gold if I book the Lite fare
2) Do I need to put my United number in the booking or can I still get the *A benefit by just showing the card? (I've got Velocity and the status credit would be more useful)
1) not sure, not really familiar with UA - however, if there is free luggage via status and you don't add the number to the booking you won't get it, which brings me to...
2) For some benefits (seat selection, baggage, etc., for instance) you would, for some (lounge access, priority boarding, etc.) you won't*.
*in theory - especially re lounge access, some of the lounge dragons might insist on the FF# granting access being on the booking, but it's not a necessity, and in my experience it doesn't come up very often these days - this is OW related of course, but I recently flew CX J and for some reason the BP didn't show my QF Platinum FF# - the lounge staff were happy to let me in on the basis of my card. They asked if I wanted to add the number to my booking (assuming it wasn't because it wasn't on the card), but didn't insist on doing it (I did accept their offer, just to make sure it was, and they confirmed it was in any case, just not shown on the BP for whatever reason, but it wouldn't have affected my ability to access the lounge anyway).
Edit - I should add that for the former benefits which do require it, such as seat selection that you only get for free because of your status, you *should* be able to add the UA number, select the seat, then switch it back to VA. The seat selection should stick. But if there's any changes to the booking and you're moved, you'd need to swap it back again to be able to re-select any seats you're allowed to only because of your status, if that makes sense.