Ok, we have a WAG today. Specifically detailing why Mab wants to ally with the White Court and is using Dresden to do it.
At this point Nemesis has strong ties or infiltrated all of the known Vampire Courts.
The Reds before they were wiped out were summoning Outsiders during the war with the White Council and timing most of their major offensives in cases Harry was handling that had Major Implications and consequences for both Mab and the state of the Supernatural world. This happened during Summer Knight, Dead Beat, Proven Guilty and is also supported by the fact the Reds were snubbing Mab by using the Ways.
The Black Court. In Grave Peril, Mavra was working closely with Bianca, who had ties to Cowl and Kumari. In Dead Beat, Mavra coincidentally she sent Dresden after the Word of Kemmerer *exactly* when Cowl and Kumori were going after it. Her motivations were hinted at Necromancy and its abilities to control Blampires, however I doubt that was the *only* reason. It seemed more like she used Dresden as a cat's paw to act on her behalf without outwardly acting against her "allies". Mavra again pops up during Battle Ground with Dracula during another Nemfected sponsored assault on Mab and the Accords.
The White Court; Most obviously and firstly, during Blood Rites where Lord Raith was helping the cult of "porn star sorceresses" use Outsider sponsored entropy curses. Madge was even possessed by HWWB.
We see White Court vampire possession by an Outsider again in White Night by Vittorio Malvora who had enlisted Madrigal Raith's help and involvement. In Turn Coat we also see Madeline Raith also be enlisted on behalf on the Traitor in the search for Donald Morgan, this works two-fold by also implicating the White Court in engaging in hostilities with the White Council. Lastly, in Battle Ground where we find out Justine is also infected by Nemesis and possessed and was able to blackmail Thomas into acting against the Svartelves, which again, brings the White Court into hostilities.
My theory is, Mab is definitely aware of this and seeking to marry off Dresden to ally the Winter Court and White Court are two fold. One, it gives Mab a concrete ally and try to cut off Nemesis' playback taking over or manipulating the White in further hostilities as they will essentially be backed by Mab and vice-versa. Two, Dresden has a knack for disrupting the plots of Nemesis and exposing their plants. Having Dresden in such close proximity to the White Court might force any other Nemfected or allies of Nemesis to expose themselves in an attempt to avoid detection by Nemesis or take Dresden out. Mab gets 3 for 1 deal, a concrete ally in the White Court, potentially getting any Nemesis plants to expose themselves or get taken out by Dresden, and third outmanuevering Nemesis before they subvert the entirety of the remaining Vampire Courts to their side.
