I do not doubt that there are many circumstances where there is a lot of suspended algae or bacteria in which case using a UV may well make the water clearer.
There may also be some circumstance where a UV might cause the bleaching of certain pigments in water. But there are many reports in the scientific literature where ozone is compared to UV (and the combination) and it is typically found that ozone or the combination is far more effective at removing colored compounds from water.
In general, a UV sterilizer does not provide the same water clarity effects as ozone. In his book "Seawater Aquariums: The Captive Environment ", Stephen Spotte has an extensive discussion of the use of UV and ozone in aquaria. In the ozone section there is discussion of the decoloration of the water by reacting with certain compounds in the water. There is no such mention in the lengthy UV sterilizer section, and n fact, he notes that dissolved organics are a problem when using UV because they absorb the light before it has a chance to get to the organisms that folks want to kill.
In these directions on how to make the most of a UV sterilizer, the specific recommendation is (with my bolding):
http://www.qualitymarineusa.com/drygoods/uv.html
"5. THE DEGREE OF UVc PENETRATION:
The effective depth of penetration of UVc in water is controlled by the following factors:
RADIANCE DISTANCE:
Complete UVc penetration in clean, clear seawater is limited to a radius of approximately 5 mm. from the lamp and this must be considered in the design of the radiation chamber.
WATER CLARITY (Color and Turbidity):
Colored water and turbid water both reduce the penetration of the UVc rays in the radiation chamber.
Dissolved organic compounds (phenolic and other organic dyes) cause aged aquarium water to become yellow.
Color removal is best accomplished by the use of ozone (ozone oxidation) in a protein skimmer, or by filtration through high quality activated carbon.
All water should be prefiltered before entering the radiation chamber of a UV Sterilizer to remove suspended materials in turbid water."
In general, it is observed that tanks using a UV often benefit from using ozone if the goal is water clarity. Folks using both often added the ozone to clear the water because the UV alone isn't adequate. Here are some quotes from folks we know.
from Anthony Calfo:
http://www.reefkeeping.com/issues/2004-08/ac/feature/index.php
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By comparison, we can look to some of the thorough research done on UV sterilizers to determine their efficacy (it is critical to pump only highly polished water through these units if they are to be effective at all). A pervasive problem that aquarists commonly face is water clarity, or discoloration to the water. How many hobbyists would you guess use ozone full-time to maintain optimal water clarity? How many aquarists change small amounts of carbon weekly instead of monthly (to prevent light shock or stress)? Some folks use no chemical media or ozone at all! I'm not saying that you need carbon or ozone to maintain optimum water clarity, but short of large and frequent water changes, there really is no practical alternative. Although your water may not look particularly yellow or discolored, rest assured that even a slight discoloration after a few weeks can reduce the penetration of light. "
from Steve Tyree:
http://www.ecosystemaquarium.com/html/tyree1.html
"The UV modules help keep the water born bacterial levels to the normal seawater concentrations found on natural pristine reefs. We also have added a very small amount of ozone to help clarify the water. I do not consider these two additions, UV sterilizers and passive Ozone use, to be abnormal additions to a captive reef system. They are used extensively in large public aquariums and I recommend their limited use on all the Berlin /systems I currently consult on and setup. The main reason these two additions are required is to break down the coral slime Reef Building Stony corals release and to prevent bacterial buildups due to this slime. Ozone is and option in tanks I consult on and is primarily used to help clarify the water which increases upper UV-A and violet light penetration. "
"
You have your air drying, ORP monitoring, carbon filtering, blah blah. Of course, there are risks with UV - number one being that you don't want water to leak into the bulb housing. Fire could result, but most likely the socket just fries and your bulb goes dead requiring new bulb and socket. Don't ask me how I know this. 
