Thanks to the hard work of Seawright over on the official 4Front OSS forums who actually the made the patch i use.

This is a modified ebuild for gst-plugins-oss as Gentoo breaks out a lot of the plugins found in upstreams gst-plugins-good package, use this to allow gstreamer to use OSS v4 (and so get sound in Gnome and its programs).

Untar this to a media-plugins folder in your local overlay (usually /usr/local/portage) . Then it should just be a case of (re)emerging gst-plugins-oss.

If once you have done this and have rebooted/restarted X and still get no sound then check that you have a /dev/dsp node. If it is missing (as it was for me) you should be able to do a ln -sf /dev/dsp0 /dev/dsp and then everything should work as expected.

Download:  gst-plugins-oss-0.10.6.tar.bz2