In a pure evil army I'll add Azelrog and Zolo Hexx, making most of my army big mean dragons. Sure aim in a must if you're using these two. Ballisters also are stupid to take. The Dragon army is fast, and it doesn't need to leave anyone behind. The familiar is not even that great for dragons, though often my army is large enough to protect it.
Evil Dragons have three big advantages.
Oboros is too good. Da'Roul is best suited for bezerking armies anyway. Garnoth is ok, but really slows the army down, and the dragons don't need a big fighter that badly. The Spiderbeast does work well. It's actually pretty mean to have the Spiderbeast and Hydra side by side.