There is a NPC in the tent at the NPC camp to the north of the tower of frozen shadow, and he wants multipl of them. Havn't had a chance to turn them all in but 2 does not work.
Duh :P Galeth Veredeth asks for 4, NOT 2 so obviously when you turn in 2 of the helms, you won't get anything. And as for anyone who tries to turn in anything less than the FOUR that he asks for, you should get a red message 'You must turn in all quest items at once in order to complete this quest.' I was able to get 2 from killing 2 ice-encrusted armsman which are light blue to me and can be snared and rooted.
Columbianspirit 70th Ranger of Tunare Terris Thule
Also, ice-encrusted armsman and deathhound do see invis but don't summon. Just like the armsman, deathhound can also be snared and rooted. Neither are they resistant to dot's and fire-based nukes