I believe special arrows scale as a % of your normal damage.
Dexterity does not affect your damage with bows. Your damage is determined by the bow you're using, +10% damage for every rank of Bow Skill.
Dexterity only affects what bows you can equip, and your chance of hitting with Bows (Perception can also be important for chance to hit with bows).
Special arrows don't do very much damage, period. You use them for their effects.
I'm not sure if special arrows' % chance of inflicting status improves with Dexterity. I do not believe so, but not certain.
I know most of them don't do much damage, but poisoncloud arrows can do a pretty large amount of damage, and you can essentially make an endless number of them if you have an ooze barrel. It's a shame that the normal damage likely affects the poison damage over time, then.
Overall, though, you are right that it is about the effects. And if the chance to create the effect is not affected by dexterity, then that essentially means that someone who put ZERO points in dexterity could actually use special arrows pretty effectively, no?
I suppose dexterity may affect the arrow's chance to hit at all (and if it doesn't hit then it cannot apply the effect), but my impression was that special arrows are essentially like spells; they don't miss; they just might fail to apply the effect.
In my mind, this makes special arrows a pretty good early-game option for any character. Early in games, the 100% chance of success special arrows have is still real good. Meanwhile, you won't have enough spells or other skills such that you aren't often on cool down with the CC spells/skills you want to use. And you don't actually have to invest any attribute points to be able to use them virtually as effectively as a dexterity-focused character. This is especially true very early on, where your inability to use anything but low-level bows is less bad since you don't have access to much better bows. Furthermore, early on, other skills won't have much lower AP costs yet, so the set AP costs for special arrows looks fine in comparison.
The only negative is that they cost a fair bit. But I find that money is not much of an object in this game, even early on, and you can craft a lot too, especially using barrels. For instance, at level 3, I was able to have 14 fire arrows, 7 slowing arrows, 5 Stormcloud arrows, 9 poison arrows, 15 silver arrows, 10 knockdown arrows, 4 poisoncloud arrows, 8 stunning arrows, 2 static cloud arrows, 1 water arrow, 3 smokescreen arrows, 1 freezing arrow, 1 cursing arrow, and 1 arrow of ignorance. That is 81 special arrows super early on.