i have done tests with quite a few types of nudibranchs while living in various parts of the tropics and had more problems trying to keep them alive! never had problems with them eating my corals, i had more headaches with nudibranchs going into the pumps and being minced up (300 ltr powerhead) and releasing all sorts of poisson into the water killing almost everything in the tank, but those were always to very colourful, fleshy looking ones.