Depends on the size of the fish, I'd imagine. They can catch and eat small snails, so if you have fry... maybe. Wouldn't think so though, mine never seem to bother/hurt anything except little pond snails and food bits, heh.
And depending on the species that's being called "ghost shrimp" they can be easy or difficult to breed.
Are you in Singapore? I know that ghost shrimp there -- unlike in N. America -- are actually Macrobrachium, which may or may not be able to breed in freshwater depending on the species. Oftentimes they are young M. rosenbergii, which can attack fish or damage them with their sharp rostrum (the spine that projects forward between their eyes) as they're being consumed.
Like others said, be careful if you plan on keeping some smaller fish in there. I noticed my neon tetras slowly disappearing, and caught the shrimp in the act at night!
Like others have noted, just make sure they are really ghost shrimp. The lfs's around here don't seem to know the difference. I've had some real ghost shrimps and some monster's that start out looking like ghost shrimp. I lost about 10 fish before moving him to his own tank, and now I feed him feeder fish