Don't fool yourself . The star do and can and will harm zoas . I witness one of them eat a zoas in front of my face. and i don't have nudis in my tank. ITs almost like havng a fish that MIGHT eat corals , 50/50 chance
A harly shrimp will eat them in a matter of no time. so getting 2 would be starving them. You would also have to get some CC star fish to feed the harly after as it will eat those little star in a few days.
this is from experience , andi believe the star was not all white had some red in it as well. they also produce in #s which could become a nuisance later on , JMO