I now have a Xoom honeycomb 3.2 and an working OTG cable. After inserting a USB stick that is 1GB FAT formatted, I find that SD Card mounted as /mnt/external1/ but the folder is empty. How to mount a usb thumb drive on Xoom tablet?
To get USB mass storage capability, The only way is root. Then you can file manager called root explorer for accessing these directories on your Xoom device. Without custom kernel or root, you can't also access FAT formatted USB drive using a OTG cable.