Yes, as gavanderhoorn said, namespacing the drivers on the ROS side should work fine, and sounds like the best approach.
My understanding of what happens inside the IRC5 controller is not as good, but I’m curious to hear how it goes for you. As I’m typing this, a festo engineer is helping one of my colleagues connect a festo linear rail to an IRC5 controller so that we can move our ABB arm around on it. We’re working through the electrical and mechanical setup now, but afterwards we’ll have to dive into debugging the RAPID code that is running on the controller and talking to the ROS driver. My plan was to generate combined trajectories for the arm and linear rail, and using one ROS driver. That would probably be overkill for your 2 arm setup though.