hmmm. never done that on a tenon shoulder. i'd back cut the face of the housing a bit and / or pare the tenon shoulder with chisel or slick. seems you'd end up with saw marks on the face of the post... no?
i've kerfed scarfs as i've pulled them together. that works well as the blade seems to take a bit from each side... but the grain is oriented in the same direction - so there is no cross vs. long grain conflict.
