There are no rules for Gestalt in Pathfinder, so there's really no way to answer this except to say that they are separate where there isn't text saying to the contrary.
2 separate rage pools i'd guess with no stat stacking.
They have the same amount of rage that a level 1 barbarian would have. Bloodrager doesn't grant any rage.
Bloodrage grants bloodrage, which is significantly different. It activates bloodline powers and you can cast bloodrager spells. You need to keep track of the two pools separately.
you can cast bloodrager spells even while not bloodraging FYI(if this was already clear then i'm sorry for the tangent). normally you can't cast spells while "raging" so they added that line.
lets say you got to lvl 4 as a primalist bloodrager/barbarian so you now have 4 rage powers do all 4 activate during the one rage?
only from the rage from their respective class