My guess is that they won't kill Ashoka on screen, ever, so her faith will remain speculative until they add a new scene to the next episode 3 re-release where you see an unnamed togruta getting gun down by clone troopers... Face it, you know it's how it will happen
For Rex, remember that his loyalty is programmed so I'm pretty certain he would have jumped on the bandwagon. And even if it wasn't the case, I'm under the impression that he would have followed Anakin's orders without questions, so if Anakin is mowing down Jedis, Rex will follow.
As far as I know, there was only one group of clone troopers that never obeyed the order and it's because they were experiencing a comm black out when it was issued. For some reason, they did not carry order 66 when comms were re-establised and became renegades, but the reason they did not fall in with the rest of their clones is speculative at best. Maybe they became out of sync when they did not follow order 66 originally? Maybe if the order wasn't given by the right person it didn't work? No clue.