In theory, yes a scarf can be cut in either direction. But to use it as a scarf, the cut would have to be made to make usage of the load bearing direction of the joint. If you cut a 7-1 ratio angle across the wide face of the strip and use that on the boat, you would not gain the advantage of what is commonly known as a scarf joint. You would have an angle cut. If you were building something with the strips placed on edge, then that same cut would be a scarf joint. How does that sound?

You're probably right but I think of the scarf in terms of it's usage and not just because it's cut on an angle.