Moderation of self-hosted servers is entirely the responsibility of the server's owners (and perhaps hosting providers, if it's extreme enough). We have no way to know what's happening on self-hosted servers, and it's none of our business.
Regardless, there is no technical mechanism through which we could block access to a self-hosted Zulip server via the web application (which is hosted by the self-hosted server itself and designed to work on both desktop and mobile devices).
For Zulip Cloud, you can read https://zulip.com/policies/rules. One of the nice things about Zulip's model is that communities that we do not want to host can just migrate to self-hosting.
Regardless, there is no technical mechanism through which we could block access to a self-hosted Zulip server via the web application (which is hosted by the self-hosted server itself and designed to work on both desktop and mobile devices).
For Zulip Cloud, you can read https://zulip.com/policies/rules. One of the nice things about Zulip's model is that communities that we do not want to host can just migrate to self-hosting.