HipChat Server is definitely supported by Atlassian. The documentation is just structured differently, that's all.
See https://confluence.atlassian.com/hc/system-requirements-for-hipchat-server-606306343.html for system requirements for HipChat Server.
The documentation you linked to is not about the products supported by Atlassian. It just refers to the supported platforms for individual products.
Badges are a great way to show off community activity, whether you’re a newbie or a Champion.Learn more
...able to use the clients After a bunch of testing (rooms, memberships, check for private message history, and most importantly - the custom emoticons!) nearly everything was looking as we needed, however...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs