Pokerroom site offerin 50% "Rakeback"

You are correct. It is total rake divided by players in the pot times times 50%. You do not have to win the pot. That was a question in a previous post. You do actually have to play the hand by either being in one of the blinds or calling the initial bet. It is not dealt hands where you only have to be dealt in to the hand and not actually play it. All the Pokerroom skins are contributed not generated/dealt to my knowledge.