The samba ebuild (tested with 3.0.14a-r2, but no change seem to be present in the later ones) does not build the libnss_* related to samba. Later in the ebuild are these files copied/linked where needed, but they are not actually built before that...
Created attachment 75535 [details, diff] A simple patch fixing the problem.
libnss_* stuff will be built if setted WINBIND flag...
with the 'winbind' flag active, the patch shouldn't be needed. Reopen if I'm enourmously wrong :-)