I legit waited to read the credits (and also to see the post-credits scene). It was indeed Mark Hamill himself. I certainly don't expect him to be a regular in this show. They didn't overplay the scene and that's also true of the other de-aging scenes. Sometimes they're just luckier in how they are able to play them. Obviously, Darth Vader is very easy to use that way.
As for Leia in Rogue One, Carrie Fisher was alive and well when that movie came out. She
was apparently aware of the scene and had seen it herself. I loved that scene at the end with Princess Leia. I can't speak much about the Tarkin scenes, but I didn't think those were bad. He was a menacing figure of the Empire and, if you've watched the Clone Wars, you'd see his beginnings in the Grand Army of the Republic.
