<p>Should it be on the development servers or a Subversion server?</p>

<p>I suppose this could be expanded to any client-server version control system.</p>

The physical repository should be on a stable system that gets regular backups.
Generally, a development server does not fit this description... it may be acceptable to put the apache server on the dev server and host the files remotely on a stable, backed-up file server (though there are a number of pitfalls with this approach) if you are unable to get additional server resources. Hosting it on the dev server may be fine if you have an aggressive backup system to protect your code...
Just keep in mind that dev servers are prone to configuration changes, being blown-away, or otherwise mucked with that could take down your repo at a critical moment.