My hoggy is in a glass tank with a screen lid and 60w light over head. I have a few live plants in with a substrate mix of eco earth, repti bark, and cypress mulch. I water the plants ever so often and that soaks into the substrate. Other than that I do not do anything special for my hoggy and she sheds just fine. I believe since she usually is burrowed down in the caves she makes in the substrate it gives her all she needs because I always find nice full sheds when I refresh the substrate. I do not really monitor the humidity level in her tank but being in the same room as my only other glass tank and knowing that one will stay near 30% without misting I would guess it is near the same.
I know that I really didn't give you a number but like you have seen I have never found a caresheet that put much emphasis on their humidity levels. When I got started with her the caresheet I found and liked was on the extremehogs.com site but it only mentions not having excessive high humidity for them and do not give actual numbers.