Yes the rage ghosts can be killed pretty easily if you have a freeze weapon.
I got about 5 of those hats yesterday.
Here is how we did it with just 3 of us pirates:
1st pirate shoots rage ghost with a pistol then when the rage ghost comes after that pirate the 2nd pirate hits him with the freeze weapon. Then the 3rd pirate kills the ghost with a blunderbuss using steel shot. Worked every time.
Note: It gets a little tougher when a bunch of people that are not involved in the plan start hitting the ghost recklessly.