Damage Reduction 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, 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.

At GM Discretion.

Damage Reduction 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, it just requires you hit, so I'd say it's fine. Obviously there's GM interpretation here of what "most special effects" means, so there is no RAW-perfect answer except your GM's ruling.