Honestly I can't really guarentee anything, that said I have never heard of a porcelain crab hurting any coral. I suppose at the most you run the risk of any hermit crab, emerald crab and such inverts of stabbing the soft flesh of a coral with a pointy foot, but not to likley.
I had a porcelain crab for a year or so, never bothered any corals of mine.
Thomas