We document all supported operating systems in the installation guide. By definition, if it is not listed it is not supported. There currently is no support for Red Hat 7 or 8 in the 7.1.1 product documentation.
Typically new operating systems are only added to the support matrix with new product version although in exceptional circumstances we may certify additional platforms with patch releases.
I am not aware of any such plans for 7.1.1 but I am not allowed to make forward looking statements about unreleased product versions. You might want to reach out to Sales who if you have questions about the future products.
