I'm feeling pretty confident now that RAW make swarms susceptible to sneak attacks.
In fact, looking at the most recent printings of the Core Rulebook and on the Paizo PRD sneak attack's description does not contain the phrase "precision damage". It makes it sound like it is extra damage stack on top of the original weapon (or whatever) damage.
The only thing I can find from Paizo that makes sneak attack "precision damage" is the definition of the amorphous creature type (unless this is more-clearly defined in an FAQ I overlooked).
d20pfsrd's sneak attack description appears to make it clear that sneak attack is precision damage:
'The rogue's attack deals extra damage (called "precision damage")'
But I can't see that the text in the parentheses originates from Paizo.
So RAW would make sneak attack damage just damage lumped into the weapon damage, which would then be ignored/halved as per swarm rules? This is my best interpretation at this point.