I must say that I disagree on that point, since a Death Knight cannot really be compared to a Paladin. Yes the Paladin does use light, healing, and blessings to his advantage, but the Death Knight uses fear, curses, corruption, and pretty much just death itself.
That is also why a Death Knight would easily be able to raise a skeleton, or even an entire army without a problem. They rule over the dead, they control it and uses it against the living.
But all in all, I think many classes are capable of raising the "undead" to aid them in battle, but that is just my opinion. I'm not good at a Lich's abilities though.