I am not for or against Dragons recieving a rez spell. Personally, I would be more in favor of dragons getting a unque skill, in this case lets call it Birth of the Phoenix, that gives the player a pop up option on death to spend hoard and resurrect themself. Give it two versions both questable. The first one at level 20 and the second at lvl 80. Let the latter version remove the DP but at a steeper hoard cost.