[Damage Reduction][1] reads:

> Whenever damage reduction completely negates the damage from an
> attack, it also negates most special effects that accompany the
> attack, such as injury poison, a monk's stunning, and injury-based
> disease. Damage Reduction does not negate touch attacks, energy damage
> dealt along with an attack, or energy drains. Nor does it affect
> poisons or diseases delivered by inhalation, ingestion, or contact.
> 
> Attacks that deal no damage because of the target's damage reduction
> do not disrupt spells.

For purposes of [Hammer the Gap][2], it just requires you hit, so I'd say it's fine. Obviously there's some GM interpretation here of what "most special effects" means, so there is no RAW-perfect answer except your GM's ruling.


  [1]: http://www.d20pfsrd.com/gamemastering/special-abilities
  [2]: http://www.d20pfsrd.com/feats/combat-feats/hammer-the-gap-combat