With the thoughts of the Gigants, I would lean more to them summoning something like Kiajai (FFVII) since they seem to based/placed in various earthly locations. Also following migration, they may have been born up in the far north, but headed towards Mor Dhona, Corethas, and even Thanalan looking for food/shelter/homelands due to whatever happened up there (Garlean invasion/slavery perhaps...)

With this thought in mind, and with Yoshi-P mentioned about the dragon beast tribe my mind doesn't to towards Shiva on this one. I get why most of you are going there, Shiva - THE ICE PRIMAL/SUMMONS/GF...of the Franchise.

My mind however heads to the gorge below the bridge between Whitebirm Front and Stone Vigil where a small, dead, snow white dragon lies. Also, based on video provided by SE, Bismark may be a Dragon, but he is white.

The aspect of "Icy" may just be a personality trait, not the basis of their primal's power.