[bmwroadsterca]

[...]

The series regulator assists with cooling the stator by interupting, and thus reducing, current flow from the stator.

That action has nothing to do with the question of whether adding additional loads with the OEM shunt regulator reduces stator heating - it does not.

In the shunt system the voltage is dragged down by drawing current. Whether the current draw is by the shunt regulator or other electrical loads makes no difference. The stator sees the total current draw and it is that total current draw that contributes to stator heating.