deathknights have some ability to summon undead, but deathknights are not necromancers as a class. So you could raise a zombie or somethign, but it will be a one or two for the sake of balance. Besides deathknights also got a whole slew of other nifty abilities aside raising the dead too. Where if you are a necromancer and you pull out the necromancy from them they turn into frail targets with no use for them. But yeah I would appreciate if the necromancy isn't the focus here. And most important point is that some deathknights do not serve the lichking which is the problem with normal necromancers who only server the lich king.