This could be argued until we are blue in the face. It has been tested with several species, but certainly not all. It is my opinion that is the life circle can go round without it, and the geckos ramain active/healthy/etc. there is no need for it (again, reminding readers this is only true under appropriate supplementation).
I feel it boils down to a matter of preference between keepers. I have found all artificial forms of UV to be absolutely useless and costly, and a very inaccurate means of determining the neccessity of UV for geckos.
Again, just my thoughts