I don’t know if Blender has an operator that sees the mesh has a hole and fills it, I’ve never encountered a situation that I needed to pay attention to that. I would’ve thought remesh closed holes in the mesh, seems like it doesn’t from what you say. I guess probably there are addons on the Blender Market that have taken this into account. Sculpt mode is fine with the mesh having a whole as far as I know, I’ve never had any problems with that when sculpting.
