I suggest smbgpradd.sh from Samba HOWTO page cxliv to be added into Samba source tarball and installed after issuing "make install" command.
*** Bug 1169 has been marked as a duplicate of this bug. ***
I don't think we should include this in the packages. too closely tied to Linxu and a specific group management tool (groupadd). Thanks for the suggestion though.