FreeDNS support has been added with the recent release of ddclient-3.8.1. Unfortunately the ebuild is missing a dependency on dev-perl/Digest-SHA1. As indicated in[1]: "Digest::SHA1 needed for freedns update." Please see to adding this dependency to the ebuild, possibly with a freedns USE flag as it is only used for the freedns update. [1] http://sourceforge.net/apps/trac/ddclient/browser/tags/release-3.8.1/ddclient#L1780
Fixed in net-dns/ddclient-3.8.1-r3.