Can someone with the Deflect Arrows feat and Uncanny Dodge deflect an attack from an invisible (or otherwise unseen) opponent?
Deflect Arrows:
You must have at least one hand free (holding nothing) to use this feat. Once per round when you would normally be hit with an attack from a ranged weapon, you may deflect it so that you take no damage from it. You must be aware of the attack and not flat-footed. Attempting to deflect a ranged attack doesn't count as an action.
Uncanny Dodge:
She cannot be caught flat-footed, nor does she lose her Dex bonus to AC if the attacker is invisible. She still loses her Dexterity bonus to armor class if immobilized. A barbarian with this ability can still lose her Dexterity bonus to armor class if an opponent successfully uses the feint action against her.
If he is aware that an invisible creature is around, yep.
First, I don't think Uncanny Dodge enters into it. Being attacked by an invisible creature doesn't cause the defender to become flat-footed, and a character can still Deflect Arrows even if he has lost his Dex bonus to AC provided he still meets all the requirements.
If the invisible creature makes it's stealth check vs perception, then the target is not aware of the attack (even if he's otherwise aware that there's an invisible creature in the area). If the character makes his perception check, then he is aware of the attack.
Uncanny would allow him to preserve his Dex to AC, which is normally denied if the attacker is invisible.
And if the invisible attacker passes his stealth check (stealth + 20) vs the defender's perception, he could attack on the surprise round, which would make the defender flat-footed, but is denied due to uncanny dodge.
But yes, since he isnt aware of the attacker if he doesnt succeed his perception check, he wouldnt be able to deflect arrows.
Regardless, the attacker would still get his +2 to attack for being invisible against a sighted defender.