A typical flat-footed creature can't make attacks of opportunity, but does a flat-footed creature still enable allies to benefit from flanking if the creature's appropriately armed? Similarly, does an armed creature still technically threaten a square even if it currently can't make attacks or attacks of opportunity, whether because it's flat-footed, exhausted its attacks of opportunity, petrified, or even dead?
It's the first round of combat. The sinister achaierai goes first, taking a double move that places it adjacent to Bob who conveniently possesses the feat Improved Unarmed Strike. Chris goes next, taking a normal move—while drawing his longspear—that places him in a position to flank with Bob the goofy Acheron-spawned bird-beast. Chris takes a standard action to make a standard attack.
Does Bob's mere armed presence enable Chris to gain the benefits of flanking the achaierai?