It is the operating carrier that counts. In this case, a standard Star Alliance redemption search wouldn't show up the Virgin Atlantic flight as an option.

You could ask the call centre to search for the Virgin Atlantic flight specifically (the CO codeshare is irrelevant in this case), but you would have to pay a higher amount for the redemption as it is on Virgin Atlantic. You also would have to book a round trip as you can't do a one way redemption on VS.