I'm not very convinced by the reasons in the OP.
1. Not only did the sign up ask if you were a werewolf, it asked about all sorts of facts about your characters that just are not important for anything other than survey purposes.
2. The good thing coming to werewolves are the skill tree, which we know they're getting with Dawnguard.
3. There really is no reason on number 3.
The companions is already a whole guild full of werewolves, no reason for there to be another. And besides, there would be no place for nonafflicted characters to go in this DLC if it was either-or.
1. Like I said before, they likely asked applicants if they play as werewolves so that it would be almost guaranteed that people will test the new perk tree, and likely test to make certain that you get cured of it properly when you become a vampire lord or something.
2. We don't know if the perk tree is going to be the extant of lycanthropy's involvement in Dawnguard, so let's not state that the perk tree will be the only thing Dawnguard will be doing with werewolves as a fact yet. Though one could assume that to be true, considering that was the only audible demand prior to Dawnguard. Not trying to imply that that was the statement you were trying to get across, I'm just reiterating important notes about Dawnguard info.
3.
Not sure one you mean on that one. I figured out what you are saying. It is entirely possible that there is new werewolf-related content that they do not wish to reveal at this point in time, though I'm not certain if that's the case. It is confirmed that they are getting a perk tree in order to balance them out against vampire lords, which literally could mean anything.
My whole point here? We simply do not know enough right now to confirm anything on this beyond the perk tree.
Finally, do you even know anything about the Companions? They are not full of werewolves.
Spoiler The Circle is initially made up entirely of werewolves, but is eventually purified of lycathropy for all but one NPC member. The lower ranking members are NOT werewolves.
Now, I don't think they should do the Dawnguard as werewolves, as that would make them too similar to how the Circle are (werewolves fighting for justice for the people, etc.), but they could always do a minor joinable faction for werewolves for whoever wants one done. There's no reason why that can't be done, so long as it's something that serves a different purpose than that of the Companions (which is more a warrior-centered guild, something people seem to keep forgetting).
But werewolf cured players need a chance to get back to werewolf to try out the new perk tree if they feel like it.
I keep seeing comments like this everywhere. Maybe one possible way for them to go at is through wild werewolf encounters? That could resolve at least two demands in one, possibly more.