conjuration is the deadric letter O. I think it's nothing more than looking cool. Morrowind's icons functioned the same way, only using dunmer imagery.
Oblivion Portals also looked like an Oth. Didn't pay attention though.
There is consistantly one actor who initially conspires with Lorkhan.
Very nice line of thought, but....
The leaper appears to be the Aurbis frivolous children. Magnus and the others were more stable. It was Lorkhans deception to appear as one of them. Another problematic point is Dagons position as King of the leapers, which would actually be Auriels position.
Finally it doesn't work well with the commentaries where Dagon was created by Magnus children to deliver them.
I give my soul to the Magna Ge, sayeth the joyous in Paradise, for they created Mehrunes the Razor in secret, in the very bowels of Lyg, the domain of the Upstart who vanishes. Though they came from diverse waters, each Get shared sole purpose: to artifice a prince of good, spinning his likeness in random swath, and imbuing him with Oblivion's most precious and scarce asset: hope.
Deathlessly I intone from Paradise: Mehrunes the Thieftaker, Mehrunes Godsbody, Mehrunes the Red Arms That Went Up! Nu-Mantia! Liberty!
edit:
Ofcourse you can bend that last bit in by noting that Magnus was the first to rebel against Lorkhan, the first revolutionary.