I know I typed a reply, but now I don't see it, so here I go again:

I don't think your dad hates his, because if his feelings of relief at his death, anger, etc. were really hate, he wouldn't be wanting forgiveness for his dad. Forgiveness is wanting a person to be pardoned for sins committed, and even though the negative feelings and consequences will always remain, this doesn't mean your dad hasn't forgiven his. Forgiveness doesn't mean all your relationship problems are gone.

No, I don't think anything positive comes from hate.