Well if that's what a vendor called them, your vendor is not describing them correctly. 405 is not UV. But neither is purple for that matter.
But that's beyond the point really. 405nm is 405nm. I guess the real point is that though you've seen no problems... That's a good thing. Because if its LED - which are very narrow in frequency range - what you see of 405mn light is only a small fraction of what's hitting your corals.
That's the nature of the human eye. We do not see true UV at all. And we can only barely see 405 nm.