Unholy dps and unholy tanking specs are very similar... the main difference is that you'll drop some dps talents to get the 5/8/5 damage reductions.
Be prepared to avoid 5% less attacks, and take about 18% more damage per hit.
If you have some decent tanking gear you can prob pull it off with a swap to frost presence in your DPS spec. If you get HoR with a weak healer and low DPS you might be in trouble. ( heck that can be trouble in T10 tanking gear LOL ) Any on use Dodge type of trinket(s) would help a lot also. That way you will have an extra cooldown to use when IBF isn't up. And save your Boneshield and use it like a cooldown also. One time I tanked half of HHoL in my dps gear and spec before my guildie healer start to complain. Shes like what is wrong with you, do you have your pants on or what? That included the powered up first boss and an extra pack. LOL She kept me alive but ><
I do not think it would really matter if you were unholy or frost or blood dps spec either, they all would have a benefit of some sort. I tank as Unholy because my 10 man group has alot of casters and they like the damage buff. When I tank heroics, I rarely have to use any cooldowns in pugs, so I think you would be fine. Try it! Get a couple guildes to go with and see how it goes. That will give you the real answer.