I think the only real question is, if the game in question can be purchased or not.
I do not know if you can add free games. Free as in, the account does not accept payments. This might have influence about revenue sharing and the purchase status of the game later. You cannot change revenue split after the bundle is created. And a game only counts as purchased if money was transferred. A purchased game stays purchased, even if the price changes from 0 to 20. And you normally cannot purchase a game that has no purchase/donate button.