I would say the same thing... I have four emerald crabs in my 55 gal and one of my emmy's tore apart my coral banded shrimp while I was at work one day. (my wife said she saw the horrific display).
Also, back to the first page of the discussion about these crabs, I definitely notice the same behavior among the ones I have. My yellow tang swoops about the tank and seemingly without tiring, one of the crabs will appear to try to "grab" the tang as it swims by. Of course, it has never gotten close, but it's humorous to observe. Interesting characters these emerald's are.