It's super illegal. Irrespective of whether you need a commercial release of the game in order to actually play Diablo with this engine, the fact is that they're distributing a derivative work of software copyrighted and proprietary to Blizzard, which is illegal under copyright law without authorization. And that's not even getting into due diligence w.r.t. other IP concerns; there could be third-party code or trade secrets in there.
There is no way this is not a derivative work of the engine of Diablo, assets or not it is blatant copyright infringement. That said I don't think Blizzard is going to make any attempts at enforcing it considering similar projects for other old Blizzard games.
It is. And it's mentioned at the bottom of the github page, too: "This work is being released to the Public Domain. No assets of Diablo are being provided. You must own a copy of Diablo and have access to the assets beforehand in order to use this software."
This seems legally questionable given that all of the source files have a copyright notice from Blizzard indicating distribution without written permission is prohibited.
Oh, sorry, I thought the comment I was responding to was nested under the 'freeablo.net' discussion, and not the main thread. You're right that this person is distributing stuff they shouldn't be. I'm guessing it will be removed from github shortly.
