The Junkers definitely have an interest in Kusari's underground as they do in all other houses, but the Hogosha agents are everywhere so Junkers generally keep out unless they know exactly why they're going in and where they're headed, then take the least amount of risks.
In gameplay, I just don't have a reason to go. There's harassing the local miners and having little to lose about it, sure. But that's not a whole lot. Also, Hogosha players generally don't bother Yanagi no matter how many artifact smugglers I intercept in Sigma-19. They'll start eventually, I hope.
The one Hogosha vs. Junkers event was a fiasco due to miscommunication. There hasn't been one since.