"I can see how going with "Nage is Uke" can lead to the statement that "the teacher (Nage) is taking ukemi", but to me that's no more than a confusion of terms. I hope the above mapping with uchidachi/shidachi clarifies my point of view.
ok, so another way to paraphrase (keeping modern aikido roles)
Nage teaches by being defeated by Uke
Now, that sounds like a sneaky way of teaching ( and the mother of all excuses for screwing up a tech)