mine will pick off a snail or hermit every once in awhile. he leaves the bigger stuff alone though. my conchs are never bothered, my CRB shrimp is never bothered and most of the bigger turbo snails are ok. like said above it is hit or miss with them, some are fine, some are fine for 1 year and become terrors, some are terrible from the get go.
i have noticed that if i place my new CUC in the rock work and keep the wrasse fed before i add them to the tank. i usually have good luck, but that is not to say he will not pick some of them off down the line. thats just the wrasse acting like he would in the ocean.
Did you research this fish any before you bought it?