There's something there, but I don't know if it actually means anything, or if all of this is just coincidental stuff just meant to show that the two worked together at one point, which we already know with the First Fight in Aldudagga. Message sent on the subject:
Warning, reaching and rambled scrambled thoughts that probably mean nothing
I'm trying to force this idea together of some connection of Mankar with the Aka spirits, Mehrunes Dagon and Lorkhan, but it's really loose at best.
First thing that I was thinking about was how some people used to think Lorkhan was Dagon, or the Leaper Demon King. Though that isn't true, so we think anyway (since, who knows, he could be an aspect), there at least is a connection.
Lorkhan's heart was taken from his chest and shot into the ground where Red Mountain rose, trapped and stuck in lava, just like how the greedy man was trapped under a mountain (interesting that aka spirits are always responsible for that. Alduin doing it the first time, then Auri-El). And Dagon's realm is surrounded by lava, brimstone and fire everywhere, with sigil stones acting as the heart and anchor for various sections to the place.
Mankar, while wrong in so many things stated, claims Tamriel is Dagon's birthright, though he also says that it was the principality of Lorkhan. He probably realizes this connection with the two somehow as well, to serve one of the less respected daedra lords. Or he thinks that Mehrunes is him, perhaps to call it his birthright. They both also go against Alduin. Mehrune's sphere of Destruction, Change, Revolution, Energy, and Ambition also is pretty Lorkhanic. With Trinimac, Arkay, Orkey and Malacath; Mehrunes Dagon and Lorkhan wouldn't be the first to have Aedra Daedra connections, though of course, Lorkhan's not quite an Aedra, but you get my meaning.
There's also Mehrunes' Daedric Crescent in relation to moons:
http://www.uesp.net/wiki/Lore:Daedric_Crescent
http://www.uesp.net/wiki/Lore:Gaiar_Alata created with the Mysterium Xarxes by Mankar, which was given to him from its author, Mehrunes Dagon, also acts a lot like his own version of Sovngarde.
Ever wondered why the blood of a god and daedra were needed to open portals to his realm? Lorkhan's believed to somehow be both, or related to both. It's also interesting that we had to use Talos' blood to open a great gate.
Anyway, so we have that, and we have Mankar thinking or wanting to be dragonborn even though he calls the 8 traitors. But not all gods associated, but maybe he knows there is a connection of the dragon to Lorkhan, and that there's a key to what he thinks is Lorkhan's principality through the Dragon, because the Dragon and Serpent are intertwined. And obviously there is, with the amulet being the key to Mundus' gate to oblivion, which I guess is the Wheel.
Ramblings that don't much mean anything on their own, but it helps to write it out. There's some connection with these four, but I can't figure it out. Or maybe there isn't, and Mankar just muddied things.
Don't even know what I'm trying to say really. I guess either Mehrunes Dagon is a part of Lorkhan, or simply a very loyal servant of him I guess. Funny that the Nords have stories of Alduin helping them against him. That's quite an irony since he consumes them, and Lorkhan actually works against him with Mehrunes. Perhaps that's the point, and because of the Dragon Cult. So they'd be aware of this as well. He was the only Daedra present when Aka-Tusk summoned those others in the Tenpenny Winter thing. Why him?
As mentioned to me, there are clear connections with the aedra and daedra, which isn't surprising given that the names truly don't mean much as far as defining what they are, and they're all just high spirits. MK mentioned connections between Kyne and Meridia, so there's that. Whether it means anything, or if it's just random associations, I don't know. I just wanted to get all that down whether it meant anything or not.