One source of material of a zako getting screen time/focus, is actually in the movie divergent. Not counting the brainwashing aspect of the movie. While there are obviously female zako in the movie, its the brainwashing that made the guards do bad things. So in this case its actually a male guard, Miles Teller's character. The blonde erudite boss lady, Miles Teller's character knows she is evil, and knows what she is up to. Yet offers to join anyway. She makes a comment "I already have enough guards".
He ends up on guard duty at the back entrance into dauntless's hideout, easily dealt with by the protagonist. What I like about his character, he made a conscious decision to join the bad guys. In this case he was kind of a coward, wanted to be on the winning side, and that was his reasons/motives. In other material a zako would join a organization say like Cobra, Hydra, Shadaloo (from Street Fighter), Spectre, and I could go on. These people join for different, and similar reasons. However one thing they all have in common, they don't mind being bad, and since in some of those organizations, they know they are one of the bad guys, they deserve being taken out by the good guys.