Just search old threads concerning UAE. I remember questioning this at the time. Somebody had a working UAE, but as I recall this didn't work with MOS.
from what luky-amiga is saying, it sounds like he just has a directory with Amiga OS in it.. I've sent him a PM but no replies... and that is why I posted this question because of his reply.
I know that command, used it too. I did have a partition used for UAE. Installed OS3.1 on it. But after a softreset in UAE all made dirs (like C and so on) aren't recognised as dirs anymore, but instead they show up as files.
Also, I couldn't startup from the drive because my used partition wasn't recognised as a harddrive in UAE.