You might believe that, even firmly , but there enough counterexamples to make that general belief unjustified.I firmly believe that an animal that does not bask regularly, is nocturnal and rests on the undersides of leaves during the day do not gain any benefit from UVB.
Interestingly, Agalychnis callidryas may not be one of those counterexamples, and there seems to be evidence that high levels of UVB (which are exceedingly easy to provide inadvertently where UVB output is not metered) is actually a health risk (increses fungal load) for the species.
"Here we used two methods of UV provision (“background UV” and “background UV with UV boost”) and two calcium gut-loading diets (5% and 10%) to assess the effects on a range of fitness measures in the red-eyed tree frog (Agalychnis callidryas). We found no effects of either UV treatment or calcium diet on growth, body condition or cutaneous bacterial communities of frogs, although subsequent to the UV boost, frogs had a significantly greater fungal load in comparison to frogs that were not UV-boosted. There were negligible differences in the breeding success of females according to UV exposure. Provision of the UV boost was not demonstrated to provide any real advantages for A. callidryas in terms of growth or breeding success. In addition, there were no benefits of a 10% calcium diet over a 5% calcium diet (in conjunction with regular dusting)."
Antwis, RE, Preziosi, RF and Fidgett, AL, 2014. "The effect of different UV and calcium provisioning on health and fitness traits of red-eyed tree frogs (Agalychnis callidryas." Journal of Zoo and Aquarium Research.
Most recommendations of this sort don't take into account the species in question ("all herps need UVB", which is patent hogwash, not only because there simply isn't data for most species we keep), and don't take into account the very real risks of potential harm whether physical or behavioral, and also underestimate the care and precision with which UVB needs to be offered to be safe. The considerations are quite complicated, and I personally like to use the most simple methods that provide the best care for the animal most reliably -- that entails no UVB for species that can be kept very healthy without it.As for the UVB, I have read mixed messages about the need for it and Vit. D levels.