Why did Draco hate Neville Longbottom

Did Harry Potter know that Draco Malfoy redeemed himself?

Yes .

Before Voldemort's death

Harry has a vision through Voldemort's eyes of Draco being forced to torture Rowle.

"More, Rowle, or should we end it and feed you Nagini? Lord Voldemort is not sure if he will be forgiven this time. . . . You called me back to tell me Harry Potter fled again? Draco, give Rowle another taste of our displeasure. . . . Do it or feel my anger yourself! "

A tree trunk fell into the fire: flames blazed up, their light shot over a frightened, pointed white face - with the feeling of coming out of deep water Harry deep Air and opened his eyes .

It was sprawled on the cold black marble floor, its nose inches from one of the silver snake tails that supported the large bathtub. He sat up. Malfoy's lean, petrified face seemed to be burned into his eyes. Harry felt sick of what he had seen, of the use Draco was now being made by Voldemort .

* Harry Potter and the Deathly Hallows, Chapter 9, A Place to Hide

Obviously, Harry is appalled by what Voldemort is doing to Draco. He feels sick about the use Draco made of Voldemort . Why should he feel sick? He knew Draco wasn't happy becoming a Death Eater.

After Voldemort's death

The Death Eaters were rounded up and taken to Azkaban. When we see Harry becoming an Auror and Draco not going to jail for being a temporary Death Eater, we can put two and two together and say that Harry knew Draco would be saved.

[...] when dawn broke that the Imperiused had returned to themselves up and down the land, that Death Eaters fled or were captured , [...]

* Harry Potter and the Deathly Hallows, Chapter 36, The Flaw in the Plan

Draco also appears in the epilogue at King's Cross to send his son to Hogwarts. He acknowledges Harry, who in turn won't leave and slaps Draco in the face.

The Witch King of Angmar

Who is Rowle? Which book are you referring to?

Mat Cauthon

Both quotes are from Sanctuaries of death . Here is Thorfinn Rowle's Wikia page.

The Witch King of Angmar

Which side is that in the Deathly Hallows?

Mat Cauthon

I edited it in my answer, we may have different editors of the book, but mine is Bloomsbury (New Edition): pages 140 and 609

The Witch King of Angmar

DavidS, disagree.