I always thought it was pretty silly to write a 110.3 on using RMC couplers for a transition between connectors. That is especially true if there is a hard wire ground in the raceway. I have heard it argued that the quality of the connection was "not evaluated" so you couldn't count on it if the raceway was the grounding path. It still sounded pretty silly to me. The reality is, I have only seen it done a couple of times anyway.
