Redeemed undead are undead who have had their souls restored to them, either through an artifact, a redemption check by a Priest of the OlderSister, or through the dark necromancies of the CryptLord.
Redeemed undead are still undead -- they are still immune to critical hits, mind-affecting spells, or anything requiring a Fortitude save. A redeemed ghoul still hungers for human flesh, and a redeemed vampire still thirsts for human blood. However, they gain experience and may progess in levels as the class that they were in life, though they have the ability scores of their new form. While a wizard who finds himself transformed into a wraith may benefit from his new incorporeality, the barbarian-wraith will be at a severe disadvantage, given that he can no longer touch his opponents unless he finds a ghost blade.
Any undead that can create spawn, such as wights or shadows, face a difficult journey as redeemed undead. Creating spawn is an evil act, even if the creatures are under the redeemed character's control and "forced" to do good deeds. Very few redeemed undead with good alignments will voluntarily use their energy drain abilities if they think it will kill the opponent.
While most people in the Twingate area know that redeemed undead exist, they will never automatically assume that an undead is redeemed. They have heard the story of the vampire who became good, but if they see a vampire, they're still going to break out the holy water.
Redeemed undead with divine spellcasting ability must generally convert to worship either the OlderSister or the CryptLord.