They're bent on pushing RHEL Server, so the message is that you can't use anything but that as a server. Or that you "shouldn't" or whatever. Either way it's a confusing mess
It's not really that bad. It's all about support and tuning and compatability testing.
Redhat isn't testing those server packages with the particular combination of packages and configuration that makes up WS. You could install them yourself, but you'd be responsible for doing your own tuning and support.
If you want to run those services in an environment where redhat has tested and tuned them for you, and is willing to support you if you have problems, then you need to update to at least ES.
It's incredibly silly to use WS as a server, because you're only paying for (and will only receive) support on the non-server portion of it. If you want support you should pay for ES. If you don't care about getting redhat support you might as well run something free, like Fedora.
