This question may have (and probably has) been asked before but I can't find any definitive responses that clearly define how the different Aid Another traits and feats interact with one another.
From a strict reading I would probably say they wouldn't but I'm not sure.
How would something like the Helpful trait that actually changes the bonus from +2 to +4 interact with the Swift Aid feat which already changes the bonus from +2 to +1? Does it overlap again? Are you granting +3 instead?
I just asked this same question earlier today, after Zach proved how awesome Aid Another could be in a recent game. :)
My interpretation is that you take the highest value, that Aid Another bonuses stack, and that a single person can aid multiple times if he gets to take multiple actions (as with Bodyguard and Swift Aid).