So after completing Dawnguard, the current state of the falmer kind of made me think about a few things. For some reason the falmer rush the forgotten vale. Is this because they knew that the vampire lord was in there and they wanted to kill him? He did freeze them all and I feel like if he had actual control over them that he wouldn't have needed to do this. The NPC also says the falmer yet have hope.

So I've been wondering how viable the idea that some of the lost or lesser races may rise up with the other races to help fight the thalamor. Im mostly thinking of the Sea Elves, Dwemer, and Falmer. If you think this may be possible or have other races that may have a higher chance of doing this, please say so.

But yes, what do you think of this idea of these lesser races that we don't commonly hear about coming to the aide of the empire or returning to tamerial?

The Maormer have pretty much always been in conflict with their Summerset cousins, raiding and pirating and whatnot in the southern seas, but realistically there's no reason to believe they could achieve much (or else they already would have). I guess if they saw the tides of war turning they would be useful allies against the Dominion.

The Dwemer are gone, but in a way, they are still fighting the Altmer, and have been for many eras.

The Falmer realistically couldn't do much. I mean, they only exist in Skyrim, are fairly few in number, incredibly weak in pretty much any arena besides tearing adventurers apart. The Nords have been living happily on top of them for eras, so I think the Thalmor are probably safe half a world away.

Valenwood's various subaltern Orsimer and beastfolk are probably a reasonable source of potential resistance, if they even still exist in great number. They're going to get the worst of Thalmor racial policies, so I'd see guerilla resistance (even gorilla resistance). Could already be genocide-d though, so who knows. Have you read "Tam Rugh Revolution"? I don't have the link right now, but it's a great text about Imga basically playing a major role in overthrowing the Imperial government in Valenwood. If things shifted around I could easily see it being repeated against the Thalmor.

None of these groups would really come to the Empire's aid - they'd be serving their own interests, conveniently lining up with the Empire's goals.

No, I haven't. It sounds fascinating. I have always speculated on "how far" Imga have developed as an independent culture and people. Theres very little known about them, besides some slightly comical comments about their ridiculous attempts to "emulate" the Altmer (whom they seem to have an avid fanatical loyalty to) - To this effect, I can see Imga being a real headache for an Imperial offensive into Valenwood, since they seem to be diehard Altmer (And therefore dominion) loyalists. They are also probable numerous. But again, of limited intelligence, since they have never emerged as a new civilisation. They are basically witty gorillas (liked the smart crack, by the way ) who can dress up. But they are also pretty scary in a fight.

Ayelids and Snow elves would both have good reason to hate the human races, and to fight against them rather than the dominion (to which would constitute almost zero advantage). I imagine the dominion would like to install an ayelid government in Cyrodill, as a vassal. Of course, that's if they even exist. But there is speculation that they do. Snow elves...I cannot see them ever fighting for the Empire, after what went on with the Nords. Theres a possibility the dominion would offer them a significant chunk of Skyrim if they fought for them. Do they actually like the dominion? Hard to say if most of them are even aware of what is going on. The Falmer, if they continue to develop, are going to be a major threat to Skyrim in the future. If they could somehow be engaged....it wouldn't be gorilla fighting, it would be an all - out war for supremacy in Skyrim. It would basically be the end of Nordic help in a second conflict with the dominion. But again, im not sure the falmer are intelligent enough to even care about it.

Dwemer are a politically isolated bunch historically. Even if they returned I doubt they would even care about the great war...mainly they would use it to their advantage to conildate a strong position on Tamriel.

Other races? Most of them [tamrielic] are extinct, or have left forever. I cant see them playing any significant part in future conflicts. I think Sloads are perhaps the one force Imperials could use to their advantages....give the sloads alinor if they launch an inward invasion. It would be the equivalent of a snow elven invasion of Skyrim.

For me, besides Snow elves, I see any intervention by lost races to be extremely unlikely. But it cannot be rules out.

I couldn't have answered better myself!