RHEL 7 was opened for download in 2014 and can be found in the "Certifications" section of MOS:
12.1.0.2 passed the certification on the RHEL7.
12.1.0.1 failed to pass the certification on RHEL7.
11.2.0.4 passed the certification on the RHEL7.
11.2.0.3 failed to pass the certification on RHEL7.
Some other points of knowledge:
1. There are also Rhel 5.10 and Rhel 5.11 versions, and I thought RHEL5.9 was over.
2. In the various Linux distributions (Rhel,suse,oel), under various Linux versions, install the different Oracle DB version must-see articles:
Master Note of Linux OS Requirements for Database Server [ID 851598.1]
However, this article does not have guidance for installing Oracle DB under RHEL7.
For an article on installing Oracle DB 11.2.0.4 under RHEL7, see:
Requirements for installing Oracle 11.2.0.4 RDBMS on RHEL7 or OL7 64-bit (x86-64) (document ID 1962100.1)
Versions of Oracle DB that can run on RHEL 7