Hypersmurf
Moderatarrrrh...
How is the check not active? You're doing something in the hopes of hitting someone. Sounds pretty active to me.
No, you're not. You're making a roll to determine if they provoke an Attack of Opportunity. You're not doing anything, and you're not (yet) hoping to hit anyone.
Until the roll is resolved, you don't have the option of doing anything active, because it's not your turn.
If your roll beats theirs, then they have provoked an AoO. At that point - and not before - you have the option of doing something active.
Also, why even make the roll if you don't want to hit them?
So you know what your available options are. It doesn't matter whether you want to take the AoO or not - when they attempt to Tumble, there's an opposed roll (whether it be an opposed skill check, attack roll, ability check, saving throw, or whatever) to determine if their action - avoid provoking an AoO - was successful.
Attempting to hit someone is in no way "a roll made to avoid (at least partially) damage or harm." That's the definition of a saving throw. How does it make sense to use a saving throw when you're not even meeting the definition of the term? If that were the way it was supposed to wrk, they could simply have made the counter to Bluff be will save + saving throw.
I wouldn't have had a problem with that.
An attack roll is "A roll to determine whether an attack hits" (glossary) or, if you prefer, "An attack roll represents your attempt to strike your opponent on your turn in a round" (combat section. Yet it's the mechanic we use to resist being disarmed.
I don't have any qualms about using a Reflex Save as the basis for determining "Was he quick enough to avoid giving me an opening?"
-Hyp.