There is also a UV-C that comes from the sun/stars, and our ozone prevents all (except a very minute amount) of this from entering our atmosphere, so it generally should not be a factor in what we are talking about... with that said, I will also say that I do not know the UV make up of electrical arcs, so welding may or may not be a source of UV-C, but it is most definitely a source for UV-B and UV-A. As for HID (typical outdoor) lights, here again I do not know the make up of the UV spectrum they produce, but I suspect it's enough to excite UV enhanced baits, yet not much more (since we don't get sunburn from these at night).
As you mentioned, black lights (or other specific UV producing lights) give us humans a loose idea of what the fish might see when our baits are enhanced with UV additives... bottom line, their definitely worth using!