You got it right with your RAC understanding. However, since u have confirmed that there are both a DEV and PRD instance running on each ibm box. And your seniors told u that they are ibm clustered.

Therefore, most likely, its the PRD instance that is going to fail over to DEV if PRD hardware has some issues. IBM HACMP is a hardware clustering failure. Why DEV is there for the fail over is so that the box will not be left idling just waiting for a fail over to take place.