A normal barbarian can't cast spells during rage because they can't concentrate during a rage. Since a Dreadnought can concentrate during rage, does that mean that they can cast spells or use spell-like abilities?
A barbarian can call upon inner reserves of strength and ferocity, granting her additional combat prowess. Starting at 1st level, a barbarian can rage for a number of rounds per day equal to 4 + her Constitution modifier. At each level after 1st, she can rage for 2 additional rounds. Temporary increases to Constitution, such as those gained from rage and spells like bear’s endurance, do not increase the total number of rounds that a barbarian can rage per day. A barbarian can enter rage as a free action. The total number of rounds of rage per day is renewed after resting for 8 hours, although these hours do not need to be consecutive.
While in rage, a barbarian gains a +4 morale bonus to her Strength and Constitution, as well as a +2 morale bonus on Will saves. In addition, she takes a –2 penalty to Armor Class. The increase to Constitution grants the barbarian 2 hit points per Hit Dice, but these disappear when the rage ends and are not lost first like temporary hit points. While in rage, a barbarian cannot use any Charisma-, Dexterity-, or Intelligence-based skills (except Acrobatics, Fly, Intimidate, and Ride) or any ability that requires patience or concentration.
A barbarian can end her rage as a free action and is fatigued after rage for a number of rounds equal to 2 times the number of rounds spent in the rage. A barbarian cannot enter a new rage while fatigued or exhausted but can otherwise enter rage multiple times during a single encounter or combat. If a barbarian falls unconscious, her rage immediately ends, placing her in peril of death.
A dreadnought can enter a dispassionate killing spree as a free action, granting her additional combat prowess. The dreadnought gains only half the usual bonuses from her rage but takes no penalty to her AC, can use all her normal skills and effects that require concentration, and is not fatigued when her rage ends. The dreadnought cannot enter a rage for 1 minute after she ends her rage, and she cannot charge or run while under the effects of her rage.
This ability alters rage.
Thanks for the confirmation.
Yeah, it's thematically neat.
Mechanically I think it's really only beneficial for multiclassing or gestalt. Taking effectively -2 Strength, -2 Con, -1 Will, and not being able to charge (no Beast Totem Pounce!) is just not worth +2 AC and being able to use all your skills normally. And when the bonuses increase at level 11 it becomes an even worse trade.
But if you're wanting to do a Rage Prophet or a Barbarian-based Eldritch Knight it might be a better bet than relying on Moment of Clarity, or Bloodrager with the Mad Magic feat.
And in gestalt it turns combinations like Barbarian//Magus or Barbarian//Kineticist from a terrible idea into a solid option.