Uncanny Dodge ability does not grant Barbarians and Rogues total immunity to losing their DEX bonus to AC. This would suggest that there are circumstances under which a Rogue or Barbarian would lose their DEX bonus.
Unfortunately, the wording in the Uncanny Dodge ability description is rather vague, and open to interpretation. However, I would rule that a successful Feint attempt would negate the UD ability, and render the target DEX-to-AC-less.