There seems to be a bug (or lack of feature) where when you hide faces of your mesh, the Skin modifier's paint weights tool will still treat those faces like they're visible and attempt to paint weights onto them. This makes it quite challenging to skin characters that have any kind of overlapping meshes such as skirts, cloaks, jackets, etc.
The expected behaviour is that when I hide certain faces of my mesh, those faces will be completely ignored by the Skin modifier's paint tool. I feel like this shouldn't be something terribly hard to fix and would save a lot of headaches from me and my animators. Thank you for your consideration.