Yep. They tend to congregate around slimy corals - zoas, shrooms, LPS where they feed off of the mucus. Otherwise they aren't a problem until they start to get thick enough to shade the corals. As long as there aren't a ton, Salifert's flatworm exit works great. Dose @ a drop per gallon and do a partial water change in a couple hours while adding fresh carbon. The drug is safe; the toxins in the flatworms is NOT.
Alternatively, a few predators include: spotted mandarin gobies, yellow coris or 6 line wrasses (most heliocoris species), springeri or yellowtail damsels, or if you can find them the black nudis with thin blue stripes (sorry - don 't know their name)