They generally do not eat corals. A story to clarify this-
I used to maintain a tank at a gym I was a member of. I started the tank from scratch and the asterina stars started multiplying. Model citizens the first 2 years or so. The asterina population was immense. Suddenly they got a taste for zoas. They were all over them and when I plucked them off there were little bite marks. I ended up eradicating them with a harlequin shrimp.
before this, I would have told you that they NEVER eat corals, but this strange happening makes me tell folks to just keep an eye on them.