ZM5: The only way a materials can be passed through ineffectually is if it doesn't exist. However, then it can't cause harm either.
You can define the wrappings as the only tissue/material aside from the organs. The game will treat it like the creature is a solid block of that material, though. Make it a very low-density one. Give the wrappings a good edge and make the creature's attack primarily by scratching; a low density material won't do much for punching.
To make a material weak to edged attacks and resistant to blunt attacks, you can use its material properties. The shearing values define resistance to being cut; a low shearing strain at break value would do it. A high compressive yield will probably help it resist blunt attacks. Not sure how or if tensile, torsion, and bending actually come into play anywhere. Bending might be important to resisting blunt attacks, i dunno.
If the creature doesn't bleed, doesn't breathe, and is immune to basic effects like stunning, nausea etc. it will be tough to debilitate. If the attempt to make it resistant to blunt attacks works, punching it or using things like maces won't hurt it too much. Blades will cut through it like butter, though. I imagine these guys are going to be fragile no matter what you do, really. If the wrapping material does resist damage reasonably well they might stand a chance, but so long as you can eventually slash their head, upper or lower body to bits you can beat them.
Meurlorg: Ghosts are a hardcoded thing, there isn't a raw tag that controls it AFAIK. Don't think you can make them eat anything inorganic either.