Duroc cement board, when abutting to regular drywall, is first to be primed with thinned mastic (4:1 water to mastic) and then taped using durabond 90 (hot/setting mud). This is what is specified by the manufacturer in their application manual, and the procedure which I follow.
Maybe this thinned mastic priming process will work in your seemingly similar situation?
Sorry, no clear answer for you, but maybe this clue is helpful.
Why do you want to primer it before you skim coat it? In high-rise construction skimming concrete columns and ceiling is standard practice. If anything you would want to used a bonding agent. BTW how much do you need to level out?
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