I think it has been shown that they can absorb calcium through vitamin D3 supplements but it's very risky. I had a few when I was a kid, no UVB and they did not develop MBD. Sometimes this is the case and sometimes not. It was standard back then not to provide UVB, it was thought they didn't need it or use it. There's better understanding now that UVB is more natural and safer for insectivores. Some books have stressed that tree frogs are particularly sensitive and could be easily overdosed on vitamin D3 supplements.

We know now that being nocturnal does not mean animals wouldn't be exposed to UVB or if they only receive little UVB, then they'd develop skin thin to allow low UVB to utilised (leopard geckos have thinner skin than a bearded dragon for instance, which allows more UVB to them at lower light levels). If no UVB, they'd find dietary D3 (nocturnal burrowing frogs such as pacman frogs are barely exposed to it and would probably get theirs in fish, frogs, snakes, rodents etc). The leaves red eyes sleep on would certainly get UVB and you gotta look at their diet as well, insects don't provide vitamin D3 and there's no vitamin dust in the wild, only vitamin D3 from the sun and inside whole vertebrates.