Just tried it again and you're right it does produce an error, I was sanitizing a real error I just had though. With the real one I had an unescaped space, cat mentioned that it couldn't open "both" files, in just gave me a message about and "ambiguous redirect"
$ < not_existant_file less bash: not_existant_file: No such file or directory
I just tried this on bash 4.3. Cat remains superfluous in this case.