"File server" vs "Microsoft Windows computers and servers"
Hello,
From what I've read both "File servers" and "Microsoft Windows computers and servers" require a Remote Agent to be installed. If that is true then why is there a dinstinction between the two in the UI? Does one option provide more functionality over the other? If I choose "File servers" does that mean I cannot backup Exchange? Conversely, if I choose "Microsoft Windows computers and servers" does that mean I cannot backup files?
When you install a RAWS in a Windows machine and it is publishing properly to the media, it will be detected and be listed as a server in BE as "Microsoft Windows computers and servers". The ability to add file servers, is so that you can shares stored on NAS which may have an OS which you cannot load either RAWS/RALUS.
why did it allow me to add the server without deploying an agent?
This is to cater for NAS. Explanation above
And why did it let me create a job and browse the file share without throwing an error?
Why not? BE went through the normal routines and they work. There is no way for BE to tell that it is Server 2012 behind the share and that it is unable to backup the share
And why did the job run (and backup a small portion of the files) at all instead of immediately failing because of no remote agent?
This is because Windows 2012 is not supported and hence not tested. The failure can occur at random points.