After trying to get Adafruit's 8x8 LED Matrix python example code to work on both my Raspberry Pi and my BeagleBone Black, I realized there is probably something wrong with Adafruit's code and not me. The matrix is working just fine with a Teensy3.1.
I decided that this is a good time to cut my losses and learn how to program i2c.
In my first steps I came across this useful blog where someone did this using the i2cset command. Unfortunately the device seems busy.
According to one person, "UU" on the i2cdetect, could mean "Probing was skipped, because this address is currently in use by a driver".
Others had also mentioned "modules" that may already be using the i2c bus, and that one could remove these "modules" and try again.