Gerrit provides its own git storage for repos rather than attaches to existing ones. This is probably needed for some internal review branch handling.
Everything else is same as git, you can work with any git-oriented tools with gerrit-managed repositories. Access to repos is through SSH keys, nothing is any different.
Adding another review tool on top of gerrit-managed repos is possible, but is indeed crazy :). There is a problem attaching gerrit on top of other repos (e.g. GitHub), however there are open-sources forks and plugins for such stuff as well.