Well that paper is very inclusive, and recognizes the cultural construction of gender (red flag).

I'd say that yes men get raped in war by other men (rarely though, who the fuck does that?), and men get raped by other men (gay ones) in peace from time to time, especially weak men by strong men.  And very rarely a woman rapes a man.  But I just don't think 30% properly accounts for all the rapes of women that go unreported.  It doesn't smell right.  I have no special knowledge here though.