if their claws look like they are designed to tear up flesh, then they probably are. the claw of a crab is a good indicator of what it's personality will be like.
As far as disease goes...
there is something to be said of that I suppose. but more towards exposing pacific creatures to gulf pathogens. most of our fish are not tank raised, and it is for certain our live rock comes from the ocean, as do many of our corals and other critters. all of this can carry pathogens, so being worried about transmitting a pathogen from collection down on the coast is, well, let's just say we should all practice quarantine.
"Maybe in order to understand mankind, we have to look at the word itself: "Mankind". Basically, it's made up of two separate words - "mank" and "ind". What do these words mean ? It's a mystery, and that's why so is mankind." ~ Jack Handey