So I was looking through the adversary section of the book and saw a number of Alliance personnel types thrown in as adversaries.

For a game based on the players being IN the Alliance I've been trying to figure out why Alliance types were included there.

Any thoughts?

As quick-reference NPC archetypes is my first guess.

Also, the game can be inverted to play as Imperials, so those stats would help with that, too.

"Adversaries" is really just the name given to the section on NPCs. They don't have literally take an adversarial position to the PCs.

There are just lots of examples of NPCs who could be both enemies or allies to the party.

So you can join the imperial side and shoot some rebel scum?

Also, this cover double agents, mutiny and internal fights.

Or sometimes you need to roll the dice for alliance NPCs...

As my GM once said after a session involving Rebels running Spice, just because they're Rebels, it doesn't mean they're the good guys. There are good Rebels and there are bad Rebels, just like there re bad Imps and there are good Imps.

Also you need them if you want to use the squad rules and mass combat rules.

Actually used them quite a bit. The first couple of missions were intended to teach the players the star wars RPG dice mechanics - so I had them undergoing basic training and being checked out on starfighters.

Hence, dogfights against their instructors (Rebel Aces).

Your PCs might wind up using social skills checks against their superiors (lying, mooching, or just straight up debating strategy)