This seems to be purely a problem with the code that shows the skins for selection in gut UI.
If I put a directory at skins/foo, I can select The skin foo.
However, if I then close the client and replace that directory with a symlink to the skin's directory, it keeps working.
Note that on Windows it does allow you to select symlinked skins.
Nothing extracted yet.
If a skin is symlinked into the skins directory instead of copied, it doesn't show up in the skin selection.