In my own personal experience with the "little darlings" I think they can be VERY aggressive..Somewhat aggressive to say the least..
If two are put together in a 55gl or less, the stronger of the two will tear the other apart..
I think that they are very pretty, but not for my tank, reef, and fish..
I would suggest a cleaner/skunk shrimp..they are pretty docile that I've seen..
I dont know personally about picking at fish, I've only seem the ones I had, (eaat different times) rip the hell out of other shrimp in my tank, and even pick on some of my reef...So I say "No Way..Jose!!"
Just my opinion
~Susie