The lift vector though is relevant.
Indeed it is, if you're talking about overcoming weight. However, you are not. You are talking about a force couple used to roll the aircraft about its own CG.
Without slip, there is no lateral stability. With slip, an- and di-hedral function correctly whether the aircraft is erect, inverted, or anywhere in between. Granted, the different "vertical-ness" of the lift vectors may make the aircraft climb or descend, but this has nothing to do with rolling couples.
Consider a model aircraft that is tied to fly along a taut wire. It can roll but it cannot slip. Will dihedral tend to restore it to wings level, if disturbed in bank? For answer, consider that for every force that you note on the more horizontal wing, there will be an exactly equal force, providing an exactly equal rolling moment, on the other wing.