I think it would have been far better to have these folks off-camera to the extent possible. To me, it's cheesy and weird to bring old or dead people back as CG characters. I felt this way about Brando in Superman Returns, and feel this way about Leia and Tarkin. BUT, I also recognize that this really resonated with a lot of Star Wars fans for the reason that Robianco and Khev at times lay it out. And at the end of the day, I think those are the kinds of fans that Kennedy et al. are really interested in appeasing. So, good move. If I were a producer, I might do the same thing. But if I were a filmmaker, with an interest in putting together something that was classy and well executed, without overt concern for the appeal to nostalgia and fan-boyism, I would not have wanted to do this, or a number of other things that happened in this film.
Having said all that, it's possible HT wouldn't have considered Tarkin if not for his video game incarnation showing up in Rogue One. So, some good can come from this even for fans of only the original films.