Charitably, they may mean "the proceeds from their endowments" (or maybe "engorging their endowments", if that's even a proper use of the word), but I think that's a weak point. Proportionally very, very few institutions have significant endowments.
You're both wrong. I'm saying they're engorged AND well endowed. Many consider this a strong point.
Oh, yeah. Some certainly are. I think they're the subset towards whom Summers is addressing his argument, in the article under discussion.