leos don't need a uth to do well. i have used both basking lamps and uths and havent seen much difference in eating habits or digestion. as long as you have the proper gradient, i think it really all depends on what the keeper prefers. some leos will do better with more belly heat, but i doubt that it is essential for most leos. my girls right now are using a simple basking lamp (60w) that I turn off at night (letting the temp in the tank drop to 72ish) and they are feeding and digesting perfectly.
either way, i think most keepers will agree that some heat source is necessary (unless you live in an area/house where the temp stays in the 80s most/all of the time).