If you have the UW pack and have a Pirate or Navy character it can not participate in the DE realm, this is due to the way the UW pack characters have a similar faction choice in terms of being Navy or a Pirate (although it is fixed to the class they pick). If it had let you join a Dragon Faction then your character would have effectively been broken in the UW realm and not able to participate.
I have no interest in changing this, doing so is unnecessary in my opinion so those of you with Pirates/Navy characters will have to settle for the unique content in your pack and not worry about going off to some new land to kill Dragons.
Yarr matey what be that, it be a dragon! Yarr fire the cannons mates!