First of all, I did do a search with keywords Deathknight minion, minion critter, dk critter, dk minion. nothing found.
Deathknights have the ability to raise a ghoul from a fallen corpse under the condition that it is a humanoid corpse or an undead corpse, however there is one mroe class they dont tell ya about.
You can summon deathknight minions from critters, such as Rabbits, frogs, skunks, deer, etc etc etc. very handy because you dont need to kill a creature your level without a minion, just one hit some little furry animal
in addition youu can also raise beasts, though i dont know if you can raise every type of beast. so far fireflies in zangarmarsh, but havent confirmed anything else in beasts
Enjoy!