Hey-I'm going to give you both ends of the spectrum on UV Sterilizers.
THE POSITIVE-UV Sterilizers are used exactly for the reason you posted. I'll make it simple and easy without getting into the terminology. It kills parasites and bacteria that flow through it. Simple as that. So in short, the answer to your question is yes.
THE NEGETIVE-I noticed in your heading that you have a reef tank. Some people say that a UV is not good for a reef tank because it kills some of the healthy particles and bacteria that corals consume. Just what I have read, but also read that they are extrememly beneficial.
In conclusion-With every other issue in this hobby there's people who agree and disagree, just one of the many reasons I like this hobby. I am thinking about getting one myself but just need to find the right one to put in between my canister filter and the tank (I know, nitrate factory, there won't be any media in there). Anyway, the choice is yours but to answer your question, it will cut down on "ICH".
peace
doug