Loren:
I was thinking along the lines of the possibility of Raspberry Pi running the object avoidance and communicating commands with the arduino.
Well in that it could be feasible, but all the actual obstacle avoidance logic (AKA "the hard stuff") would be done on Pi. So for questions about that you'd probably want to go to their official forums. An Arduino would still be useful for controlling the motors, but that's relatively simple compared to visual object detection and ranging.