The git_drush module currently provides a Git core API layer for Drush modules that use Git functionality and some Git deployment commands we are developing for our own organizational deployment needs, that utilize Git submodules. I am thinking that the Git deployment commands will probably get separated in the future into a git_drush_deploy? (not sure on the name) module. So basically there would be a Git API module with no Drush commands, and the Git deployment module that used the API module.