Yes, they have.
Last time I checked, we needed sigc++-2.0 >= 2.0.12 (as you quoted),
and again, last time I checked, the latest sigc++ in fink was 2.0.11.
I suspect that people sucessfully compiling Inkscape are using their
own sigc++ and installing it in /usr/local or some other prefix that
is searched before /sw. This does in fact, work for me. I will update
the page now, with this info, but we really need some guidance for
what advice to give to Mac devs who have been relying on fink.