I see no reason not to use a UV Sterilizer on a reef tank.
Here's the WRONG reasoning people have used before regarding UV.
It kills food that could be used as part of the food web. And then they proceed to add DEAD food to their tank on a daily basis.

Beyond that, Dr. Adelaide Rhodes (who knows more about bugs than most obviously) has stated numerous times that UV won't kill most copepods nor amphipods.