Do corals need UV to to survive? : No. Plenty of tanks with coral and no UV. Is it a gimmick, or does it help? : Not sure. Based on absorption spectra, it does appear corals can utilize the UV end of the spectra. My opinion: It adds to PAR, much like adding more royal-blue would. But it is less visible, so you can increase PAR without making your tank so blue. A bonus. Also, the wider and more varied the spectrum, it seems the better corals can adapt to light levels. (Maybe) So overall, probably a good thing. But worth spending a ton of money, probably not.