*Does the Aid Another "attack" (especially those such as the one needed for Bodyguard) suffer from miss chances due to concealment?
*How about other bonuses such as cover?
Everyone confounded on this one?
Attacks of Opportunity suffer from concealment, and the Aid Another action is described as an attack roll. I would say that it does suffer from concealment.
On a related note, total concealment would prevent a creature from using Bodyguard, as Attacks of Opportunity cannot be made against creatures benefiting from total concealment. Greater Blind-Fight clears up the issue.
It's easiest to apply this when there is "universal" concealment, such as fog. I imagine the AC 10 required for Aiding Another involves interacting with the enemy creature, so enemy-specific concealment should also come into play (open for debate).
I can get behind the cover bonus being applied to the Aid Another AC, but I'm not ready to put down anything definitive on that front just yet.