I think Moe subconsciously used his Right Forearm to guide his Takeaway. Certainly, he did not let his Shoulder Turn drag the Club deeply inside ('under Plane'), and despite his extreme Extension at Address -- his Left Wrist is fully Uncocked and his Right Arm is very straight -- his Right Elbow folds nicely during Start Up.
Moe was very conscious of the Straight Line Baseline of his Inclined Plane and constantly referenced it in his discussion of the Stroke. In fact, he often told the story of how, as a teenager learning his swing, he placed a coin well back along the Line to make sure he stayed On Line during his Backstroke.