I made some tests short time ago and it definitely works for anonymous users - I see no reason why it should not work for other authenticated users.
In my tests I hit an issue when I tried to open exactly the same document within short time frame from different devices - I looks like the docs are blocked/accessed for some time after the previous device stops editing.. but it is definitely possible that different users collaborate on same file at the same time (see referenced screenshot) maybe there is some logic issue when you access same file as same user from different devices..