Never had a problem with the emerald crab, but 3 LFS said orange and purple lobster (cant remember name) were reef safe. Not the one I got, he loves eating corals and wasn't picky about which one either. Traded him in for something else.
The larger Blue leg hermits are killers. I have the large Mexican Turbos and when one isn't on the glass, he's fair game for the blue legs. Heard my kids screaming at the tank one day and the blue legs were eating and ripping apart a live Turbo. Looked like fire ants on a carcass carrying parts of the thing back to there homes. Gotta get 'em and send the to the ref.
I just wanted to add that the lobster you are referring to is just a plain ol' reef lobster or at least that is what they called it when I bought it. I love this lobster, he doen't bother anything and he is a beautiful orange and purple. For a long time he would hide in the rocks but now he is use to the tank and ME so he will come out and greet me a lot more.
I would have to toss arrow crab on there as a borderline one, did great with all my corals but got territorial with other crabs and shrimp and would go after any type of worm in there, including feather dusters & x-mas tree worms