Using the syntax:
   Fsys.umass fsys -l -n Direct-Access=usb
I can get a usb0 to show up in /dev.

However, I can seem to do anything with it.  A mount like:
   mount /dev/usb0 /fs/usb
justs hangs.
The USB memory stick's light is on.

I had lots of trouble with this. Here is a script I have devised to open different USB sticks. I have several sticks 
with specific items on them. Each manufacturer seems to have a different device name.

  use vedit and put this into a file I call it "loadusb" then put it in the /usr/local/bin directory. Use chmod +x to 
make it executable. 



#! /bin/ksh

# Use this file to mount a usb memory stick may be run using ./memstick then
# finishing command manually depending on the type partition on the device
io-usb &
Fsys.umass -v fsys -Nusb -nusb0. & 
mount -p /dev/usb0.0             	 # check /dev/to see partiton type
sleep 2

slay -fQ Dosfsys                     	 # needed before running Fatfsys.
slay -fQ Fatfsys                     	 # needed if Fatfsys is running from sysinit.

Fatfsys e=`ls /dev/usb0.0t*` 

sleep 1

echo ""

echo "    USB device loaded as /dos/e"
 
echo ""



 Use this script to unmount it so if you want to install another disk you can do it without rebooting; Make sure you put
 it in the same directory as above and make it executable.

#! /bin/sh

# makes it safe to remove a usb stick and allows reinstall without reboot
sync
umount /dos/e
umount /dev/usb0.0
rm /dev/usb0.0
slay -f io-usb
sleep 2
echo ""
echo "    Safe to remove USB device"
echo ""


I can post a tar file with both files later if you need them

Brad