Vegeta: Destroyed entire planets for the fun of it. Afterwards, settled down with a wife and children.
Gajeel: Literally crucified Levy and her team. Enjoyed what he did. Afterwards, became good and was willing to die for the same girl.
Orochimaru: The most despicable character in Naruto who revelled in mad schemes. At the end, he helps the good guys beat Madara.
Zuko: Went on a mad manhunt for Aang and betrayed their trust. Became their closest ally shortly after.

Even Peridot was evil before becoming good!

So yeah, still too early to rule out a redemption.

Zuko is an entirely different level of redemption since he was wreck with guilt.