Another noteworthy thing is that, while HB might not do as much as an Oblit, and HB from Rime is free damage--so it can be a huge boost on bosses if you get a normal proc rate.
You really need to elaborate though. You are wondering if you should be using Oblit more. One STs, you use it as your primary FU attack unless you need to refresh diseases. Blood Runes should be turned to DRs just to get another Oblit. You will use 1-3 per rotation. The only exceptions are those unfortunate times where you NEED to hit UA, for whatever reason, burning your second Frost Rune with no DRs.
On Multiple targets, Oblit is used to put threat spikes on targets, and for a chance to proc Rime.
But, I do think your build could use some help. For one thing, with average intro-level gear in FP, you should have somewhere around 20K armor. That is 111 AP for every point spent in Bladed Armor. You don't need to take all 5, but you may want to consider some--it is a decent boost.
Icy Talons is still debatable. On one hand, if you have no Shaman and several melee in your group, it is a sizable bonus. But, if you don't, it isn't worth 6 points, in my opinion, for a DK. I hate taking talents that are only worthwhile half the time, but I'll concede that taking them is often wiser. Personally, I leave it alone in my builds, unless I know I can expect a party with no shamans and a lot of melee. But, since EVERY party I have had at 80 includes a Shammy of some kind (I have a feeling Dalaran Alliance just has a LOT of them), I mostly ignore it.
Another point people disagree on--but I find Hungering Cold to be nearly worthless. For one thing, 99% of the time you would find it useful, you don't have the RP. And wasting a glyph for it is not an option. Second, it isn't very effective against mobs in normal instances at 80, from what I've seen, so I doubt it'll be that effective in Heroics. But, like I said, some people really like it.
Epidemic. Now, I LOVE this talent. It makes me stress less when things go wrong and my diseases are ticking. However, I find 2/2 to be nearly worthless for Frost. For one thing, HB refreshes your IT on multiple targets, so it'll never be needed there. On single targets, with a tight rotation, you can definitely get in 3 oblits and a FS in 8 seconds. 1/2 is all you need.
Merciless Combat. I'd leave it alone in a build that takes IT. Just too much elsewhere to get.
So, if you wanted to keep IT I would do something like
this. The points in Bladed Armor and KM should be balanced to personal taste. You have 7 points to split between to 5-point talents. KM = more crits on Frost moves. BA = higher damage on most Frost abilities, plus higher white damage. 5 points would be about 100 damage added to HB, then boosted by talents and multipliers.
But, if you don't mind losing IT, you can use
this (14/52/5)--my current Frost tanking build (it is offspec to my Unholy one, atm). Well, that is my current one, but I'm 99% sure I'm gonna move the points out of subversion. I'll put one in Epidemic, I know. The other, I am debating between Rune Tap and Virulence...