It’s Imperial March not Darth Vader’s theme song. The Imperial March is in Episode 2,3, Rogue one and even Solo: A Star Wars story. In episode 6 it’s used when the Emperor arrives at the Death Star. Playing the Imperial March for the Revisited’s grand reveal of the Death Star is fitting. That being said, Rogue One Death Star music is fine. Whatever Adywan thinks is best for the scene.
I think the fact that it was played subtly and gently at Vader’s death speaks volumes of its association with him.