i didn't think so for a while but I used to be able to put fish with ich in my tank and a couple of days later it would be gone.... Without a uv light I couldn't do this crazy thing.... All the fish would get it...
you can use it but to say you must use one... no you don't have to have a UV on any aquarium. Like 1ucky says there are arguments either way. I've used them and I've done without them with success. I find that if I'm planning on having a lot of fish in the aquarium it make me feel better to have one on the aquarium. Does it make a beneficial difference? You never know.
A U.V. in a reef is up for an unresolvable discussion. But if you have a quarantine tank it's a useful tool. Fish only systems very helpful and ponds necessary.
Is it going to make all your fish healthy and happy... no, but no filter will.