I would say, NO, they will not hurt anything like that. The biggest threat they present is to other hermits and snails. Scarlet reef hermits are much less aggressive in my opinion and experience, and either way, both are reef safe.
I really like my scarlet crabs - they are more active than the blue ones.
You might see them crawl over the corals but they won't harm them. Scared me when I saw this at first - I thought they were eating them.
Miles