Here is my opinion.
Keep the area in which your UV is completely black and isolated, keep the UV several feet away from your return to tank and the most important, do NOT setup the return of the UV directly back into the tank, make a loop to go back into the sump or refugium. This gives the proper time of the water to settle down of sorts. Marine bio guy is right, the UV will travel up the tubes just like fiber optics travel light. Create a loop to settle the UV light down.
I have found that the UV does more good then most think because if you change your water properly and often, you should be fine.
I have never seen a properly installed UV cause anything but good things especially if you have any type of algae blooms.
I always recommend a UV when setting up a new tank because if green hair algae gets hold, it can take much longer to get rid of then doing it right to begin with.
As some suggested, there might be some chemical changes, but if you keep your water changed properly, then it should never be an issue. I can only see this being an issue if regular water changes and improper placement is done.
I have used them for years now and they have always been great IF and I say IF, used properly. I do use one with my octo and it seems to be very successful.
Just my 2 cents worth.