Should enriched doughs pass the windowpane test?
Yes it should - sort of.  

Your observation is right on point, a very rich dough will tear more easily. (I did the same experiment once myself.) But it will still show some characteristics of the windowpane test: it will stretch smoothly and the "pane" should be very even, not show streaks of thicker and thinner areas. Note that the temperature of your dough and thus the consistency of your fat may have an influence as well. While warm doughs with soft fat will be very stretchy, cool doughs (made with cold ingredients and little yeast for an overnight cold raise) can be less cooperative.

If you are familiar with how a "ready" non-enriched dough looks that passes the windowpane test, you will probably recognise the same smoothness in an enriched dough anyway, without performing the test. 



For this specific recipe, I guess it's the very low hydration that makes the windowpane test difficult and the dough prone to tearing, not the fat.