at least some are edible [to humans] when they are soft. Most harden to a wood-like texture sooner rather than later. I've used them in terraria with no KNOWN issues. I doubt that anyone has actually tested their toxicity with respect to any herp species.
Remember that each species of herp responds differently to different toxins, and there are many different bracket fungi. Knowing with certainty is effectively impossible at this point. On the other hand, if you're not soaking it in the water of an aquatic species and not housing it with an herbivore, it's unlikely you'd ever experience issues anyway.