Is Mac OS X supported through X11? From what I have heard that means that the program does not act as a Mac program, but as a Unix program.
No, Mac OS X is supported via Carbon and AGL, and application using the Mac OS X port of GLFW are proper citizens of the Mac OS X desktop. No X11 required.
However, you can use the X11 port on Mac OS X as well, if you for some reason wish to do so.