Just re-listened to the section, and it really strongly implies that Durai was one of the released prisoners. But it doesn't say that explicitly. And Latch's statement could still work if Durai was the mastermind on the outside, rewarding Scratch for releasing his imprisoned colleagues. I'm not saying that's the case here, just that I haven't found anything that makes it impossible.
And it didn't have to be Durai. The outside mastermind scenario could have been some other person who we've never seen, who might not even have survived the outbreak. That person could have ordered the RPG from Burt, bankrolled Scratch's jailbreak plan and provided the manpower to loot Locked & Loaded.
That would make a lot of sense. I see two possibilities about how Scratch came to be second-in-command and those are either (A) Durai was the mastermind and Scratch was the one that was going to be doing the springing, or (B) Scratch, Latch, Durai & co were all in a gang. A very, very violent one where everyone got busted. It might be a long shot, but if Scratch sprung everyone - Including Durai, who is assumed to be the gang leader - she would then let Durai keep control of his gang. Then she got second-in-command for saving everyone's life.