Most asterinas are harmless. Some ARE coral munchers. They tend to be larger, and have bits of red on their backs. The munchers are rare, but I've seen a few in my day.
Remove any that you see, and yes a Harlequin shrimp or two will clean them up - just be sure to rehome the Harlequin(s) when you run out - or be prepared to buy them sea stars for food.
Jenn