Peter,
The "Drive Type" option is a wrapper around the GetDriveType Windows API. If you pass an UNC notation to GetDriveType, a trailing backslash is required. It should then return $DRIVE_REMOTE$ in your case.
For example: \\ServerName\Drive\
If you still get $DRIVE_NO_ROOT_DIR$, please see:
http://support.microsoft.com/kb/244089
Does this help?
Friedrich