DBH Oh sorry, I forgot to answer your other questions:
Death Knights: Not needed. You can pick up whichever ones you like, but the normal Skeleton Mages will do just fine. As long as they cast Sacrifice you're gucci. The most important stuff from Skeleton Mage tree are cast speed, the extra mage and after that just go for survivability / leech. You just want them to survive and sacrifice the Warriors as fast as possible.
About Dread Shade: It is still used and just cast on one of the Mages. It will buff all of them as long as they are inside the Aura.