How do I hack the OWI Robotic Arm Edge available from Amazon and Jaycar..?
From what I can see from the listing it runs at 6V, and 5 gearmotors (presumably small DC motors)
and unspecified method of position sensing (if any). There is a hint it just freewheels off the range
of movement to avoid stalling the motors, so I suspect the controller just turns the motors on and off
and there is no position sensing built in.
In other words lots of posibilities I suspect, if there is mechanical room to add encoders and the like.
Bear in mind I've never seen one for real so a big pinch of salt required.
How do I hack the OWI Robotic Arm Edge available from Amazon and Jaycar..?
Can you explain in more detail what you want to do with the arm? If you want to control the arm with an arduino, then maybe a relay board to control the motors might be of use.
Design a custom 5 axis dc motor driver shield for Arduino and add limit switches, potentiometer and/or encoders to each of the joints 
.
Does no one know how to google any more? Seriously, OP - first two hits on google for "OWI-535 Arduino":
Hi gozilllozzy, I'm excited to say I am also using the Arduino Uno for a science project involving remote control of the OWI Robotic Arm Edge! Before I respond, I want to clarify, what are you trying to do? Are you trying to use Arduino to remotely control it, or convert the controller to one using Arduino, or what? It might be easier to come to a conclusion if you would specify what you are looking for. 