Whether or not they fly the same is impossible to determine -- in theory, having bubbles ever-so-slightly changes the balance of the disc, which should -- in theory -- affect flight. However, as we all know, there are countless variables in disc flight even among discs within the same run. The higher the speed of the disc, the wider the range of variation within a run, it seems.
So for X-outs, there is no way of knowing how the imperfections may affect flight, but what I should say is that I have never thrown an X-out disc that was outside of the standard-deviation in flight characteristics for a given run of discs. In theory, X-out imperfections have to affect flight somehow, but the effect is so much smaller than the other variables, you'll never notice it in practice.