Interesting you should ask!
My G/F had aquired a 40 gal SW setup a few months ago and one of the inhabitants was a Zebra Hermit. This thing would harass any other snails and crabs it could. It had killed a few snails and crabs ... even a small queen conch to get the shell.
She got frustrated, wanted to get rid of it, so I put it in my 5 gal nano. It immediatly went after any other hermit with a larger shell, in one case took over another hermits shell and then changed his mind and went back to his original shell. I guess he cant make up his mind! So, I took out every other hermit/snail of the nano leaving just him. I'll try to post a pic of this little devil tonight.
so ... I guess the bottom line is: if you get one, keep an eye on it, mine is VERY aggresive