I'd be cautious about using Hemlock for any joinery or scarfs, except the most basic kind. It is very "shakey" wood and tends to split off portions of itself very readily.
Some people call it "rot-resistant" but based on my observations I think that is a misconception. It is quite strong however. I often use it for simple purlins and joists, as round poles flattened on the top.
Sills might be the best place for the Hemlock, since simple lap joints might be enough. Save the white pine for the fancy scarfs.
Good luck.
Pete
