You have to check availability through the airline where you have your miles. I redeemed Emirates miles for an award on VX. Economy seats were difficult to find but Main Cabin Select was easier. Best thing to do is to call HA and ask what class of service they use to book awards on VX. Then you can use
www.flightstats.com or another such website and check availability yourself if HA has no online mechanism for checking availability for VX awards.