If I'm understanding you correctly, you shouldn't have a problem. While the packages may be aimed at the final release, they are all built against one of the beta/RC releases.
Hopefully, deps should be handled. If not, let the packager know. There have been a few instances where packages have been built against against things that have changed (though I think most of them relate to 5.9 rather than 6.0).
For 6.0, it would be a good idea to limit your use of packages from the gsb repo, since they may pull in a lot of Gnome related dependencies that you don't really need. OpenOffice is a good example - don't pick the one with gsb in the filename...