Nope. Sometimes they can grow an potentially smother a coral but it's super slow and easy enough to just scrape them off. I've got tons of them under my rocks. At one point I had a big one growing on a euphyllia stalk and I scraped it off just to be safe.
Edit: If it look to you like the acan is shying away from it or stressed out, just gently scrape it out. No harm no foul.