actually, this is not a good representation of wing chun sparring. chi sau is a game we play that helps us develop our attack and defence techniques. sparring from a chi sau is not really appropriate. the only other person you will expect to do that is a wing chun trained person. unless you hang out in a wing chun school, you are not likely ever have to defend against another such trained person. crossing and rolling hands will get you into trouble.
I remember watching a video where the WC guy just walked into the ring and immediately tried to cross hands. the other guy just knocked his brain out.