Hi RJ,
I think you are right, an angled hole would work, as long as the angle didn't take the bottom of the hole too close to the bottom of the inside of the slide. I haven't actually seen a Rohrbaugh yet, so I don't know how much metal is there.
Years ago, when I asked Colt about putting tritium sights on my Detective Special, I was told that it could be done with the front sight only, because there wasn't enough metal in the rear sight to drill without weakening it excessively. This, of course, is a very different situation as the rear sight on the revolver iis part of the topstrap.
The picture looks really nice.
I am a big believer in tritium sights, and if it can be done without unduly weakening the slide, I'd do it in a heartbeat.