Judging by their voices (when they’re singing) it sounds like they’re mostly males.
But there are extremly many Hyenas.. Shenzi couldn’t have been the mother of all of them?

I always thought the majority were males unless proven (by voice etc) otherwise. But looking at the main 3 Hyenas in the Film, Shenzi is quite easy to spot but in "be prepared" all of the marching Hyenas looked the same. I think they left it to the viewer's imagination, using the same design for each Hyena as a metaphor.