I think it's probably fine. I can't remember exactly how oval the frames I've seen this on have been but 0.5mm doesn't sound like too much. If the cups go in all right and then the bearings turn smoothly in the cups you're good. I did have one frame (MTB frame with very large diameter and quite thin-wall HT with brazed-in rather than pressed-in cups) where the frame's ovalness was squashing the cups a bit even after they'd gone in and making the bearings bind. But a little bit of persuasion with a vice brought it back round enough. I doubt you'll have this problem with a road bike frame though as the cups are smaller diameter, longer, fatter and generally more chunky so it would take a lot of force to distort them. But worst case the vice is probably the fix not the reamer.