I think it's Destiny's Force, which super-great soundtrack. I'd love to hear it again in KH3.
(I'm not sure atm because the OST playing for the Blue Tail Raid Boss is The Encounter from KH2 xD)
Nope. It's actually the battle theme that plays when you fight the Shadows during Sora's Station of Awakening. It's called Fragment of Sorrow.
But yeah, KHIII should reuse some KH classics. Since this is the last game of a saga, I expect it to deliver some throw backs to the first and second KHs.