From what I understand, NT's DFS looks and acts like UNIX-style directory mounts (i.e., instead of assigning a drive letter to a shared drive, the drive appears under an existing directory).
Sort of. Microsoft have some pretty good DFS write-ups on their web site. Try starting out at:
http://www.microsoft.com/NTServer/fileprint/exec/feature/DFSWP.asp
As Mark already pointed out, a filer is perfectly capable of playing the role of a leaf volume in a DFS tree (sometimes also called a downstream volume).
Keith