Of course, the user running trac-admin must have write permission to the whole environment. In the standard configuration (both SVN and Trac served via HTTP by Apache), this is usually the case, as the apache user has write access to both the SVN repository and the Trac environment. But if you access the repository e.g. through svn+ssh, you will have to set up sudo.
But in your case, you say that the apache user doesn't have write access to the Trac environment? I thought mod_python would run under the web server's user, isn't that the case?
This is pretty much an InstallationIssue, but we should add a note about su TracRepositoryAdmin. I'll do that.
