Raoul, ya beat me to it.
Jabba the Hutt employs bounty hunters and body guards, not soldiers or sailors. There may still be a sociological disinclination for these aliens to enlist as regulars, or they may simply be relegated to same-species units which have not been depicted onscreen.
Yes, but bounty hunters and body guards are essentially soldiers for hire. The question was whether or not aliens actually are as "militarily inclined" as humans are in the SW universe. Humans very well are bounty hunters and body guards as well in the SW universe. And also you forget about the Gamorreans. They are a very warlike species. Their tradition is to be warriors of all sorts.
The point remains that onscreen, the Rebel Alliance exclusively employs humans in its starfighter corps and its ground troops. Furthermore, evidence of unit segregation is evident in the fact that Mon Cals are the only visible crew of the Mon Cal capships.
That is NOT true. You only see human pilots in starfighters in space, but when you look at the bridge of the
Home One where the Rebels were briefed, you'll see many aliens. At least two Sullustians piloted starships in the Battle of Endor. One was Nien Numb, Lando's co-pilot, and the other was Ten Numb, which is always mistaken as Nien Numb in the briefing scene. And the reason why only Mon Cals were operating their controls was because they were not modified to be operated by humans yet. And even looking at the Jedi Knights, the overwhelming majority of them were aliens. They all fought like bloody hell. Aliens apparantly have the same tendencies to fight as humans do in Star Wars.
Regarding the Neimoidians: they serve only as very high-ranking officers. The same goes for the other members of the Confederacy, except for the Geonosians.
Except for the Geonosians? That still contradicts the fact that you are arguing aliens are not as "militarily inclined" as humans are. And besides, "militarily inclined" can mean anything from being a grunt to a commander. ALL of those aliens of the Separatists were "militarily inclined."
So, if you choose to not accept the "demographics" explanation of Dr. Saxton, the other two still apply.
Well, I just explained my reasons why I object to the "demographics" reason.