Normally a git repository is not treated as a special remote, but as a git remote of the normal kind. Two exceptions to that are git-lfs and gcrypt special remotes.

But it is possible to register a git repository as a special remote. git-annex and git will use the remote the same as any normal git remote, but its url will be recorded in the repository. One benefit of doing this is it allows git-annex init to autoenable the remote.

To set up such a special remote:

git annex initremote myremote type=git location=ssh://... autoenable=true

Now git annex init in each clone of the repository will autoenable myremote.

This only works for git repositories that have a git-annex uuid set, because special remotes have to have a uuid. So it cannot be used with git repositories that are not git-annex repositories.