I don't think the hitman is in the dream reality, he doesn't interact with any of those characters. Some "reality" elements are intercut with Diane's Betty dream (e.g. Dan in the diner). Oddly Adam is the only character who seems to have continuity/identity through both worlds, although several faces repeat.
And no, I don't think that the old couple "represent Adam and Camilla" any more than the diner waitress Betty/Diane "represents" Diane/Betty. The whole film is about twinning, representation, offset realities, dream logic.
― assert (MatthewK), Monday, 26 April 2021 03:28 (three years ago) link