(With a touch more work, you can also maintain your own changes, and have them 3-way merged in automatically.)
As for not using source control - if they don't use it internally, that's a bit weird, but maybe there's just one person working on the code, and they take a backup every hour, and they're happy. (It's their time, not mine.) But not exposing their source control to the outside world is absolutely standard. I worked as a programmer for software companies for ten years and never once saw 3rd-party code distributed any way other than zipped up source drops. (And this includes times where we were working with the 3rd party on the same project! - we just did the thing I mentioned at the start when they sent us updates, and they did the same thing at their end. It's much less of a bother than you'd think, though the first couple of merges can be a bit painful.)
If you want to claim they're being unhelpful, the insistence that you upgrade at a moment's notice is much worse. Upgrading 3rd party libraries is one thing you never, ever want to do, unless your hands are absolutely tied!
Conversely, GitHub is full of low quality software.
None of this is to claim that he's a bad cryptographer, or even a bad software engineer. But pure code output is far from the only important metric for software. GitHub makes it easy to do release engineering well, or to let other people help you with that if it's not your forte. (libsodium, for instance, is on GitHub.)
That depends on your job. If you are a software developer, -engineer or similar, I would argue that you should. There are good arguments for version control.
- divide & conquer for bugfinding - reconstruction of history - being able to revert back to an older version if/while operations require it - it allows tracking of changes over time - it is the best way of understanding what changed since the last version (for people actually using the library) - finding complex faults - branching and merging (but the author is opposed to this)
So, well, what concerns live555, IMHO it's a huge red flag for people considering to actually use the library. When it comes to "not seeing an issue with not using source control", I believe that one can state without a doubt that it is a good and proven practice.