Hailing Nitram doesn't seem to stop his advance anymore. So the suggestion to hail him to keep him in place while you clear the dragon's room no longer works.
Fortunately, the mobs in the dragon's room don't seem to add to the fight. You can move your group right to his corpse and wait for Nitram to show up and wake up the dragon. Be sure to turn the dragon away from Nitram so his frontal aoe doesn't kill the gnome.