Assuming that you actually have a good Frost DK tanking spec, these are the differences between the two:
Vampiric Blood vs
Unbreakable Armor
Will of the Necropolis vs
Improved Frost Presence
Blood has
Improved Death Strike
Frost has
Acclimation
On top of all of that, Blood brings
Hysteria, which is an awesome DPS boost to any Rogue or Feral in the raid.
(Frost DK DPS as well xD)
Overall, there is a CLEAR difference between, especially when there is a Boss like Lich King or Halion 25m Heroic that will almost constantly be dropping u below 35% where WotN will shine the most.
There is a good reason why END GAME guilds, ones that kill 0% Lich King 25m Heroic on a weekly bases use BLOOD DK tank over FROST DK tank.
They also use Prot Warriors for the lulz, so I guess any tank can work there if healers are good enough, but this does not change the fact that overall:
Will of the Necropolis + Vampiric Blood + Improved Death Strike,
are better than:
Improved Frost Presence + Unbreakable Armor + Acclimation...
P.S.
"Unbreakable Armor (1min CD) ( God POwer)"
I would like an explanation on how UA is "God POwer".