The opening fictional blurb in the Operation Revival Trials shows the Adder Khan at the time giving an impassioned speech about how the Clans in their entirety should invade the Inner Sphere. Give each Clan a dedicated role, so that they can cover each other's weak points, and they'll more likely be successful.
Nearly every single other Khan decries this as the stupidest thing they've ever heard in their life, and the Adder Khan feels a little crushed by this. Ulric Kerensky doesn't say anything but gives the Adder Khan a knowing look.
Ulric being a planner himself, it would make sense that he respects the Adders (who plan for EVERYTHING). But I felt like there was something deeper going on. My current headcanon is that Ulric wasn't, strictly speaking, a Warden. He was an Adder Style Crusader: if we're gonna do this thing, we're gonna do it right. I kinda want to believe that Ulric and the Adders possibly had an alliance in the works. Maybe they worked it out so that the Adders were the back up plan for when the Invasion started to fall apart. Because once the Invasion starts, Clan society starts changing, and the dominoes start to fall, leading to the Wars of Reaving, which lead to the Adders being on top.
But that's probably me reading too much into it. I do enjoy the idea that there are some Clans who are/were playing their own long-cons. And that several Clans who thought they were clever (Ravens, and ESPECIALLY the Vipers) weren't nearly as clever as they thought, being outplayed by people like the Sharks, Coyotes (who I maintain are still up to some kind of long plan, possibly with Wolf assistance), and the Adders.