Ok it works with 6.3 but not 6.4. I guess it just misses a symlink :)

[t@blob ~]$ yum clean all
Loaded plugins: changelog, kernel-module, priorities, protectbase, refresh-
  : packagekit, security, tsflags, versionlock
Cleaning repos: ai6 ajenti ceph ceph-testing epel glusterdotcom
  : google-talkplugin oc6 slc6-devtoolset slc6-devtoolset-debug
  : slc6-devtoolset-source slc6-extras slc6-os slc6-updates
Cleaning up Everything
[t@blob ~]$ sudo yum install ajenti
Loaded plugins: changelog, kernel-module, priorities, protectbase, refresh-
  : packagekit, security, tsflags, versionlock
http://repo.ajenti.org/ng/centos/6.4/x86_64/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
Trying other mirror.
Error: Cannot retrieve repository metadata (repomd.xml) for repository: ajenti. Please verify its path and try again

[t@blob ~]$ sudo rpm -ivh  ajenti-repo-1.0-1.noarch.rpm
Preparing...  ########################################### [100%]
  1:ajenti-repo  ########################################### [100%]
[t@blob ~]$ cat /etc/yum.repos.d/ajenti.repo
[ajenti]
name=Ajenti
baseurl=http://repo.ajenti.org/ng/centos/$releasever/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-ajenti-packagers