I will say that your tank is beautiful, just not designed with dart frog care in mind. Not enough land mass to support a dart frog, especially a predominantly terrestrial species. Your frog looks to be male to me. Males are typically leaner than females and it looks like the toepads are wide which would further support my theory of male. The frog is lean though, even for a male. I wouldn't call it emaciated. Just underweight especially compared to many of the obese frogs I see posted here....and some of my own historically. I won't attribute the leanness to the environment specifically, but it is likely a contributing factor.
Dart frogs don't need standing bodies of water to bathe or swim in. They are found on the forest floor, predominantly in leaf litter. Some are found around water, but they do not use it as a retreat from predators where they need to dive beneath the surface to avoid predation. They simply associate with water since it likely provides ambient moisture, humidity, and probably a food source as insects metamorphose and leave the water. No need to metamorphose your feeders in your viv since you are no doubt feeding cultured flies. And cultured flies are easily dusted with the proper supplements. Bioactive doesn't meant self sustaining. You need to supplement your feeders to ensure proper nutrition.