I've used Midiox and the usb/midi converter cable tons of times, I mean all I usually have to do is make sure the Roland UM1 is selected as input & output. I can flash the UNO to just send MIDI (to only test TX) and still get nothing in MIDIOX. LED flashes on the Olimex shield, but as near as I can tell nothing is coming across the wire.
To clarify, when I said that I saw data in serial monitor, that was when I still had the usb cable from PC->UNO plugged in. It was not the USB/MIDI cable. The serial monitor won't work for my tests because the serial is being used by the midi shield. Any serial communications sent or rxd by the UNO must go through the MIDI shield. Know what I mean? 
That's why this is such a challenge. I can't monitor the serial communication. All I have is MIDIOX. I tried using a USB monitor, but it didn't pick up anything. I dunno. It would be great if Olimex would respond.