This is true. However, my understanding is that UV lures don't require a fish to see in the UV spectrum. UV lures are merely a specific type of fluoresence...defined by excitation by one wavelength of light resulting in emission of a different (and longer) wavelength of light. The distinction is that in traditional fluoresence both the excitation and emission wavelengths are in the visible specturm whereas with UV the excitation is not visible (but the emission wavelength is visible).

So, if you are fishing under conditions where only UV light is present, then a UV lure should be easier to see because it will emit visible light. Traditional fluorescent colors would give no added benefit.