Dodge bonuses stack. DMG, page 177, top of the first column.
In your example, the bonus is +3. Note that you lose all dodge bonuses to AC when you would be denied your dex bonus to AC, like when you are flat-footed, for example.
Bonuses that stack:
- Dodge bonuses
-The armor bonus from a suit of armor and the armor bonus from a shield.
-The enhancement bonus on projectiles and projectile weapons.
-Circumstance bonuses from different circumstances.
Wasn't there a thread some time back where someone listed out all the instances of like bonuses stacking? The "like bonuses don't stack" rule ended up looking very porous....