Real reptiles are the proof for this. As well their behavior when exposed to UV demonstrates this. UV lights have caused captive reptiles to go blind.
The problem with UV bulbs for reptiles is that the pet industry developed them for making a consistant income from customers, you see animals do not make much money, drygoods pay the bills and make money, so when the reptile industry convinced people that they needed those way overpriced bulbs they gained many customers who buy new $20-$100 bulbs every 3-6 months like clockwork. Now consider that those bulbs cost the industry $2-$20 each, thats a huge profit, so you ask why do they continue to scam and lie to the public, that $18-$80 profit per sale per bulb makes alot of those people very happy.
On top of that, the average customer spent $20-$50 on a reptile, and many products that go with it. They wont tell you that you could build a good cage, put real useful substrate in it for next to nothing, use $2-$5 lightbulbs from a hardware store, and buy bulk frozen food etc when you could be spending thousands in extra cash in the petstores.
Good husbandry is needed with reptiles not magic bulbs that can do more harm than good. You see if you really wanted to use UV bulbs you must use them in such a way that they are an option, not forced on them, they must be mounted up and away but easily acessible to the animal, yet the ability to escape it at any and all times and not to have heat from said light to effect the overall temperature range in the cage. You can by all means use them, but you need to realize that they are not needed, and that they must be used carefully.