As stated the Opera boss is locked to your instance ID the moment you enter the instance, loot tables work in exactly the same way.
Originally Posted by Jeleh
Run it on alts until wolf boss pops up - use a friend to get raid ID - join on your hunter - profit.
To get around the instance ID lock this is the answer you're looking for, just make sure you avoid entering the instance on your hunter until you have an ID that you know has the Wolf boss up and waiting to be killed. You'll first need to kill Moroes in order to unlock the theatre but as I say don't do any of this on your hunter, once you have an active instance ID for a vanilla or BC content its sometimes not possible to switch.