The Brine King + Absolution skill gem

In my fight with the Brine King while using the Absolution skill gem I noticed I was not summoning any Sentinels of Absolutions despite the odds of at least getting one of them off of 25% per hit should be high.

Is the Brine King not being read as a unique enemy?

Was the Brine King not being "hit" from Absolution? As it states, 25% chance to Summon a Sentinel of Absolution on Hitting a Rare or Unique Enemy.