Yes, OSX (at least 10.4) ships with a native Tk implementation, and the Perl Tk modules compiled against that. No need to fire up X11. (I rarely launch X11 on my mac.)
have the Tk modules. However, TCL/TK is indeed native, and doesn't use X11. I'm not sure how you would build Perl-Tk against the native Tk Widgets, since Perl-Tk includes its own standalone copy of Tk.