Fun concept! And now I want make an ex-Scarlet hunter. Only this one is (naturally) Forsaken and has only hale and hearty human-type pets, as befitting any member of the living races and—
Undead what?! You're sorely mistaken. Your mind has been twisted by the plague! We must purify you...
But we're talkin' about you. I'm not sure what your hunter is like, but the first theme that jumps out at me for an ex-Crusader (and current friend of the Light) is
virtue-based:
Charity
Hope
Piety
Amity
Constance
Faith
Grace
Joy
Mercy
Temperance
Patience
Providence
Felicity
Purity
Honor
Zeal
The theme could reflect anything from loving redemption of your plagued pets to teaching your enemies the meaning of charity at the jaws of a rotting juggernaut. It all depends on the personality of your hunter.
Another thought would be to name them after heroes of the Crusade, like those found in the
Hall of Champions. And perhaps other Crusaders who didn't end up with monuments, like
Fairbanks.
Some pet suggestions for families you don't have listed. Not all strictly plagued, but definitely plague-related:
