There are pigments in corals that experience excitation with UV-A light, and emit visible light...
http://www.advancedaquarist.com/2006/9/aafeature/view
The thing about using UV light is that the bluer you go, the more energy is in the light, so its easier to get photoinhibition with UV light, due to its higher amount of radiation (this is as per a conversation with Dana Riddle).
Most blacklights are of little use to us based more on their actual output than the benefit of their light. There is one exception though... and expensive. OSRAM/Sylvania makes a line of 150watt UV-A induction lamps... about the same efficiency as Power Compact (60 lumens/watt which is actually very good considering its a UV-A bulb and such narrow output). This kind of output would no doubt photoinhibit alot of corals though.
Ill try to find the thread, but its about 3-6 months old and involves dicsussion on the effects/benefits of UV-A in bulbs... the Giesemann Pure Actinic bulbs and halides in particular.