OKAY after researching Bair a little bit more. I think I have a theory as to why it seems like it has very very good priority.
Okay, 1 frame before Bair actually comes out, Wolf is REALLY scrunched up. Basically it's like the Bair animation except without the foot and leg sticking out. This means that if an opponent's hurtbox is within the range of that foot before it comes out, but not quite to Wolf's hurtbox, he gets hit. So basically the leg goes from not extended at all to fully extended. If the developers wanted to say... make it transitional and make the extending part transition into fully extended, I think Wolf would be considerably more crappy. However thank God that isn't the way it was done. This may be why Bair might clash into Marth's Fair, because by the time Marth's Fair reaches Wolf's hurtbox, Wolf's foot is also in Marth's.
I honestly think all of Wolf's body is his hurtbox during Bair, it's just his claws that are disjointed. But can anyone test if you can hit the foot or leg of Wolf during his Bair animation?