I don't think that Apple would sue if you did a MacOS X themed Apache GUI for the MacOS X version of Apache. However, I am sure that they would sue if you created a MacOS X themed Apache GUI for Linux, Solaris, Windows, BSD, etc., GPL or not.
There are Apache GUI projects outhere. Commanche is the one I've heard of most. The Apache GUIs aren't MacOS X themed. Apple would probably hammer them with a lawsuit if they were. You can find out more at http://gui.apache.org/