I've been trying to run UMSDOS as my root partition for the last week or so. I posted to the debian-user list to see if anyone knew about how to make this work, but I haven't received a reply yet.
Debian definitely doesn't support UMSDOS as root out of the box. I can get tantalizingly close to having a working system, but odd things are happening (like perl disappearing, or shrinking down to 24 bytes or losing its executable status). Normally, UMSDOS has been quite robust for me, so I suspect that somehow when used as the root partition under Debian it has some problems. If you don't specifically want to run Debian (which I do), you should check out the IronWing distribution (do a search; I don't have the URL handy). It's designed to run out of a UMSDOS root partition, and it works quite well. It's a Slackware derivative, but it knows how to handle RedHat RPMs, so you should be able to install what you need. Steve