The article focuses on universities' investments in hedge funds specifically. The numbers in the article suggest that on the high end, about 10–20% of an endowment will be in a hedge fund.

The question I have is, what are the typical returns just on that 10–20% investment?

The endowment can do poorly (as bad as or worse than an index fund) as a whole, even if the investment into hedge funds is paying out well.

Any discussions of returns must necessarily consider the risk incurred to achieve that return.

Sure, but (by most metrics) hedge funds are going to be riskier/more volatile and you have to lock up your money for longer. So the same return would count as worse performance if placed in hedge fund (and that's not even accounting for differences in expenses yet).

Hedge funds as a group are only risky and volatile compared to mutual funds. Their degree of riskiness varies tremendously, and there are a great number of them that would offering investment management that is tremendously less risky than an index fund.