I'd need to see more photos to be able to determine if the hognose is underweight, and if so, to what severity. In general, I find hognose skin/scales to feel more "loose" or less taught than many other snake species. They should always feel like they have a little extra room in their skin so to speak; these snakes should never feel firm like a ball python etc.

Hope to see some more pics of the snake outside the enclosure!