I'm assuming that if the spell's been cast and the holy weapon of "ZOG" or whatever is allready attacking, it gets an aoo? Don't see where it says no anywhere in the spell description.
I'm pretty sure a spiritual weapon does not flank. As such I would rule that it does not threaten, and that would mean no AoO. But I think that's RAI, not RAW.
I reckon I just ruled that it's posible to aoo with a spiritual weapon, since I didn't see any verbiage expressly forbidding it.
I think you guys' inferences were good, but my own personal...I guess preference makes me nervous to infer stuff kinda.