I use a UV sterilizer in my reef to help 1) prevent disease outbreaks in the fish; 2) control unwanted algae; and 3) promote water clarity. Thus far I have had no sick fish, minimal algae, and the water has remained crystal clear w/o the use of carbon. I'd say the UV is doing its job. Moreover, I have had no coral losses or disease since introducing my first corals approx. 2 1/2 months ago. Perhaps this will change over time. I do use DT's phytoplankton and maintain a feeder refugium, so this likely compensates for some losses due to the UV.
Respected aquarists such as Bob Fenner advocate the use of ozone and/or UV in a reef. Other equally respected aquarists view them unfavorably, at least w/ regard to reef application.
IMO, using a UV creates some of the same difficulties as heavy skimming. As there is no established "right way" to maintain a reef, it's really up to you to consider the advice and recs of others, balance that with your own experience, needs and budget, and make your own judgment call.
Again, IMO, in maintaining a reef, 1) top notch lighting; 2) an ample supply of quality LR and LS; 3) a refugium; and 4) a good skimmer are all more important than UV/ozone.