Michael

Scrimgeour and Slughorn really don't get a "redemption". They both stay pretty much in their boundaries. Scrimgeour wanted to do whatever he had to in order to defeat Voldy or at least keep spirits up, not giving up Harry's location just fit in that box. Slughorn was as evil as Umbridge was a death eater. Slughorn was an example of a good teacher that helped the wrong student.

SNAPE WASN'T REDEEMED FOR BULLYING EVERY STUDENT HE COULD ON A CONSTANT!!!!! Snape wasn't redeemed just because he loved Lilly, why does everyone forget how he treated Harry, not to mention anyone else that wasn't a Slytherin, throughout the ENTIRE series until the end. Even his help came from Dumbledore's request.