So, I only really played through BM once before even though I play Morrowind quite frequently (Solsteim just isn't incredibly appealing to me, mostly because MCA makes it a royal pain in the ass), and the second time through I'm picking up stuff that I have questions about, so here's a couple.

At one point you are tasked with killing an Aesliip, a Draugr. If you ask anyone on Solstheim about Draugr, they say that Draugr are Nords who have been turned into undead by the All-Maker for cannibalism. This makes them seem just like another mindless undead variety, much like skeletons and zombies. Now, when you talk to Aesliip, he calls the rest of the Draugr dim, and tells the story of how he became a Draugr, and that was through his own power in Necromancy so that he could preserve the barrier (which will lead to my second question). Now, when talking to him, he is obviously sentient, which would make him more like a lich than either a zombie or skeleton. I know it's been asked in this forum before, but what exactly is a Draugr? Is it just a blanket term the Skaal use for undead, or do they have some special properties that, although keeping Aesliip in the same group, make them different from other undead?

Now, Aesliip discusses why he is there, and that is to maintain the barrier that keeps the "Frost Daedra" at bay, although when one enters the cavern, they are just Dire Frost Atronarchs. It was mentioned in another previous thread that Frost Daedra and Frost Atronarchs were not the same. I know that in Daggerfall there are Frost Daedra and Frost Atronarchs, and that in Battlespire there are Frost Daedra and not Atronarchs, while in Morrowind and Oblivion there are just Frost Atronarchs, but is there anything to indicate that Frost Atronarchs aren't a variety of Frost Daedra? Was Aesliip just using Frost Daedra as a blanket term rather than, specifically, Frost Daedra?

You already mentioned the most relevant information on the Drauger and that's all there is. That he retained his wits might have something to do with him making himself a Drauger because that is the only obvious difference between him and the other Drauger.

The second part is mostly gameplay and it doesn't really matter which way you look at it. Whether the Dire Atronachs are actually Frost Daedra or not, they're cold and try to invade from Oblivion so they're now the same thing.