I think I read in a Kirkbride "Ask me Anything" on reddit that the Dunmer and Redguard are the two exceptions to mer and men. Unlike the other elves, the Dunmer do not see Lorkhan's trick as a punishment, but as some kind of blessing or at least a welcomed competition. Meanwhile, the Redguard, unlike the other men, do not see Lorkhan's trickery and the creation of Nirn as a gift to men, but as a trap from which they have to escape via worldwalking to find the strange angles. 

I think that, as far as we know, that only members of the pro-Lorkhan races (the Tribunal and Tiber Septim?) have ever realized the nature of the universe and escaped Lorkhan's trap. However, once doing that (the whole CHIM bit) Vivec and Tiber Septim returned to their mortal bodies in Nirn with the power/understanding of gods, and used this power to affect Nirn to various degrees.

By contrast, the Dwemer are the only ones we know of who thought Lorkhan trapped them and (possibly) escaped. And as far as we know, they just went away. I've always understood their disappearance as an attempt to un-create themselves in order to return to some essential form of the godhead. If that's the case, we have two different models of how mortals become divine in the Elder Scrolls: they pro-Lorkhan races manage to someone maintain their own identity while obtaining godhood (and therefore desire to return to Nirn), while the anti-Lorkhan races erase their identity and merge into some kind of godhead (and therefore disappear from Nirn).

As far as Yokudan mythology goes, it seems to fit more with the anti-Lorkhan races (the elves). Ruptga views Sep's bargain as a trap, declines to go, and later kills Sep while releasing his hunger (similar to the death of Lorkhan in Aldmer mythology). Ruptga then leaves the spirits to find their way back to him. What's notable is that when the spirits make it out of Sep's world into the Far Shores, they don't return to that world as gods (with the exception of Hunding, who seems more like a Shezarrine than a god); instead, they wait for the world to be devoured and a new world to be created. This doesn't fit with the other man (Tiber Septim) and Dunmer (Vivec) who achieved divinity and sought out CHIM, and then returned to the world. 

Short version: the Redguards are the men who see creation as a negative, and that's why their mythology (in broad strokes) looks a little more like that of the mer than that of the other men.

Great write-up; it's a really useful primer to Redguard mythology.

Just an observation: I've read that Satakal shared similarities with Alduin insofar as their intended role is to devour the world and restart a mythic cycle. However, Sep's dead skin seems to have more in common with Alduin as we seem him in the game.

We know that Alduin the god plays a divine role in the cycles of the world, and I think it's strongly implied that even though the player defeats Alduin the dragon, the god will still return in time to devour the world. Accepting for a moment that their can be a difference between Alduin the god and Alduin the dragon (which doesn't seem outside the realm of possibility, given how many avatars there are in the Elder Scrolls), we know that he hungers for souls and is able to fly to Sovngarde to feast on the souls of the dead there.

Meanwhile, Sep's dead skin can only slink about the earth or hide in the void, trying to devour the stars. I thought I had also read that Sep's dead skin/hunger chased souls that were trying to find the Far Shores, making it that much more difficult for them to get there. If that's the case, Alduin the dragon's behavior closely matches that of Sep: Alduin slinks about the mortal plane (because he has returned before it's time for Alduin the god) and Alduin devours the souls of the Nords in Sovngarde.

We see Alduin through a Nordic perspective, but is there any reason to believe that he wouldn't also devour the souls of other Men/Mer? If so, it's possible that Alduin is devouring the souls of Redguards before they can find their way to the Far Shores (I don't think he's in the Far Shores in the same way he's in Sovngarde, because I don't think they're comparable places--happy to elaborate later). Alternatively, if the Redguard creation myth describes the struggles of the other races of men, we can look at Alduin as devouring the souls of Nords before they could ever find a way to move at strange angles and escape the cycles of Alduin's hunger. Either way, there's a parallel between Sep's hunger and Alduin the dragon.

One last thought: as you explain it, Sep is made from the discarded skin of Satak/Satakal. That'd imply that Sep has some of the power of Satak/Satakal, including its hunger for devouring in the world (that latter bit isn't just implied, it's pretty clearly stated). So we could imagine a parallel between Sep as a corrupted form of Satakal, and Alduin the dragon as a corrupted form of Alduin the god. 

And the races that want to discover Lorkhan's secret (most humans, the Dunmer) seek to realize they are dreaming as they continue to dream, while the races that want to escape Lorkhan's trick (most of the Mer and the Redguard, according to my idea below) want to wake up from that dream.

The Godhead. If you're familiar with some Eastern traditions, it's inspired from them.

The unconscious first dreamer. Anu, from whom sprang Anu and Padhomey, The ultimate being. The universe. Reality. Whatever you want to call it.

Everything is a Dream within a Dream within a Dream. Lorkhan saw the way to escape the current dream, but couldn't or wouldn't. So he created Mundus and Nirn as a way for others to see what he saw and escape this dream by creating their own. An entirely new dream unlike the current one.

The Yokudans and most Elves want the opposite. To go back instead of forward. The Dwemer have gotten the closest and destroyed themselves.

More of a branching tree of universes.