I'm not what epic game policy on adult games, they allow games with adult content and adult themes in their store, but not sure about adult games with sexual content as the exclusive focus
however, they offer a monetary insentivation to make games exclusive to their store, unlike steam that you need to pay to upload there, epic pays you to upload on their store and no in steam, and I heard through the grape vines that they waver any fees for UE4+ for the first year of sales if keep as an exclusive