Well someone is out there, handing out summoning rituals, magic books and wolf- skin belts probably just for the hell of it to sow discord. Almost as if they were a Demi- God of discord resident in Chicago. This may be Nameless/Cowls weakness, he can’t help sowing discord even if it isn’t part of a larger scheme, like undermining the Winter Court with the Nemesis Athame, or seeking out The Word to remove the qualifier from god, or setting the White Court and White Council at each other’s throats. How many of the events in Chicago that have impinged upon Harry are due to Nameless indirectly?
I have suggested he pushed Maeve in Summer Knight towards her course of action, did he hook Marcone up with the Church Mice and then alert the Denarians just for fun? Was he behind the dogknapping of the puppies? The Circle/Black seem to have been behind it in Zoo Day. Before Changes Nameless/Cowl may have been responsible to some degree for most of Harry’s Files, some by design, some just for gun.
It's worth noticing, I think, that the whole "Black Council" thing -- Harry's name for Harry's theoretical group (and maybe Eb's) -- is largely based on circumstantial evidence, on inference. Note also that the "Circle" mentioned in the conversation between Vito & Madrigal doesn't seem to exist: Vito went to Cowl, and
their conversation made it clear that Vito was explicitly misleading Madrigal, who had no idea what was actually going on. Also worth noting on this topic is that Harry doesn't know
anything about the Grey Council, or who is on it, besides what he gets from Eb (and that he saw Odin at Chichén Itzá); if Eb is a bad-guy (or just trying to protect Harry by keeping him in the dark (where have we seen
that before?)) it could be that Eb thought a nice fat non-existent conspiracy (with lots of meaningless coincidences to investigate) might be better than having Harry cast a wider net.
It doesn't actually seem like there's more than can be explained by (as you suggest above) "a demigod of Discord resident in Chicago" (it's
also worth noting, though, that Greek Eris & Roman Discordia were female -- I'm sure Jim knows this! -- and wondering why Nameless
isn't female ... ). He can get outsized results -- and a variety of results -- by powering-up the low-level mortal casters, and by manipulating the bigger powers, etc... thus making it SEEM like there's some "Black Council" (or "Circle") at work... thus schismatizing the White Council.
Throwing some extra discord into Chicago, onto Dresden's shoulders, also thus isolates him from the White Council, and even from the Grey -- Discord for everyone!