Did you download the deb package from the non-free repo sun-java6-jre, or the package from Sun itself? The make-jpkg command is from the java-package package from the contrib repo, and like some Debian specific tools it requires a fully functional apt installation, so it does not work on dCore.
But I am polishing the rough edges on support for extra repos like non-free and contrib, wheezy-backports, deb-multimedia, etc which should help make available a wider range of packages to choose from that will benefit all ports and reduce the need for hosting custom ones. It should be in the next release.