reposync'ing (or pulp syncing) RHEL7 repos on RHEL6 hosts.

How can this be done? Can I subscribe a RHEL6 host to RHEL7 repos?
I am actually able to sync the RHEL7 OS repo through pulp on a RHEL6 host, picking up the files from the CDN.
Other repos, for example the extras repo, won't work for some reason.