I've never kept C. ferrugata, but it is my understanding that they are similar in behavior and temperament to C.bispinosus. I have kept several C. bispinosus over the years with corals long term (5+ years) and it seems to me that provided they are fed frequently and have adequate live rock to graze as well as some nori, they don't pick at corals. If you don't provide those, corals will likely become a menu item at some point.