My mind just kicked into overdrive for about 13 seconds and I believe I may have made a connection but I'm not very familiar with the rules on this forum in regards to "leaks" or "spoilers."
I'm not a beta tester, and what I would like to say is purely concocted from putting together information that has already been made public at E3.
That said, should I be clear of any fire with what I'm about to say?

Speculation is completely allowed.

In that case, here goes nothing.
Okay, well, we've all seen the Werewolf perk tree, and on the left tier there is a perk called "Totem of Ice Brothers"
In multiple E3 videos, Todd Howard mentioned that the Dawnguard could make use of armored trolls, though he didn't go into detail.
By now, I'm sure many of you have heard the Werebear rumors and speculation that the Dawnguard are Lycans.
Well, maybe this perk allows Werewolves to summon armored Frost Trolls, which would not only fulfill the promise that the Dawnguard could ally themselves with armored trolls, but it would also confirm that the Dawnguard are Lycans, because it is a Werewolf specific perk.
Looking at what I've just typed, I can see multiple flaws in this logic, but it was worth a shot.

It's possible. However, the logic rests on how the "Ice" in "Ice Brothers" is interpreted and whether the Dawnguard would have anything to do with werewolves...

True. Here's something else that just popped up in my mind. Everyone is assuming that Werebeasts and Vampires have a feud but let's push that theory aside for a moment.
We know from ES lore that the Volkihar Vampires (confirmed as the Vampires in Dawnguard) sometimes dwell under frozen lakes. Maybe this perk calls forth Vampires to help in battle. (A long shot, but at this point I'm just shooting the breeze)
In all honesty, it probably just summons some regular ole' Ice Wolves to aid in battle.

hmm, that connection was quite a long shot, but i see where you come from, it's as good as any speculation.

Your argument makes no sense.

The creatures in the video look nothing like trolls, and they are wearing no armor.

So it makes no sense that this would link them to Dawnguard.

If anything I'd say this supports a Lycan faction.

(Of course it could be that Bethesda misnamed the creatures for the game, but I doubt it)

i believe that's more of an accurate guess. but while we're talking about the volkair, are there anny frozen lakes in skyrim? can this ability to move through the ice without breaking it be an ability they possess?

Maybe, and there is the dragon jumping through a frozen lake in the trailer. Also, I didn't know they were confirmed Volkihar. When did they say this?

No, I'm referring to when Todd Howard says "as a member of the Dawnguard, you can summon an armored troll"
I wasn't referring to a creature actually shown in a video. And I detailed my openly out-there connection above. I said it was a long shot, haha.

Well, their castle is called "Castle Volkihar" so I kinda confirmed it myself. Lol.

not trying to demean your intelligence, I know it came off that way.

this. they are definitely Volkihar.

This wouldn't confirm them as Volkihar though. The odds of them being Volkihar are up, of course, because of it. I could easily infer they are some new strain from Atmora that took over a castle that used to be run by Volkihar, now couldn't I?

hmm, but that would be more unlikely, would it not? bethesda loves to use already established lore and expand upon that.

I GUESS you could, but... let's say you killed a man named Carl, and you took over Carl's House and made it your own. Would you not make a point to change the name to reflect its new ownership?

Ah-hah! Exactly my point. Unlikely and yet very much possible...

on a house maybe, but on a Castle? Castles usually have their own characteristics, you'll find toons of castles in europe named after their first owners, and not their current

European colonizers often used Native American pre-made names for places they came across. (Alabama, Mississippi, etc.)

I would want it to be known that I claim ownership of said castle. A name change would DEFINITELY be in order.

Now you're just being too insightful. Lol.

i'm not sure if it is tradition to change the names of castles when they get new ownership

Ok but if you're just summoning a normal troll how does that fit in with ice brother?

It seems to me the Ice-Monster in the trailer fits the bill for Ice-brother alot more then a troll.

( I know and I'm trying my best to shoot it down lol).

Maybe the Volkihars were friends of these new vampires, and the new vampires wanted something to remember them by...

Im pretty sure that i heard something about the vamp leader being named lord Volkihar.

and i think your just arguing for the sake of arguing.

'bows' It's what I do. But seriously, that was an unnecessary detour. Can someone link me to the confirmation of his namesake as being Volkihar?