Hi,
I got the same exact issue. It also tried mirroring the repositories (w/ reposync) and I’m getting the same *.el6* packages as in the tarballs.
I could install HDP 2.3 on RHEL7.1 anyway, though I got a yum dependancy issue on snappy (version in RHEL7.1 is more recent that the one shipped with HDP).
I would love to see someone reply on the official RHEL7.x/CentOS7.x support status.