Do militaristic civs have higher probabilities of getting military leaders from elite units, or is it only promotions up to elite that's easier to have?
Technically, they promote to Elite easier than non-mil civs do. They have the same probability of generating leaders that non-mil does. But considering they should have more elites, you should see more leaders with a mil civ since theoretically you'd have more elites engaging, and therefore more rolls of the dice to generate a leader.