I don't foresee Uther holding a grudge and taking delight in seeing his old pupil suffering eternally. Those were the final words of a heartbroken and very angry master, but Paladins are like the Jedi of WoW. They don't take pleasure in seeing other suffer, even their enemies, and especially an enemy they once loved and regarded as almost a surrogate son of sorts. Once he arrived in the Shadowlands and saw that his suffering, Arthas' actions, and the people of Lordaeron's suffering is like a grain of sand in a sea of stars as far as how important they are to the overall cosmology of all existence, it's likely he feels a little more humbled and less vindictive towards Arthas.
Everyone's suffering seems like the focal point of the universe until they realize how little they mean in the grand scheme of things, and in this theoretical afterlife that is the Shadowlands, being betrayed and dying by the hands of your pupil hurts a little less when you realize there is indeed an afterlife, and you have a chance to be reborn and/or ascend to a higher plane with the Kyrians for living a noble life all the way to the end.
A good Paladin like Uther would see this.