Because they're both part of the Fediverse, Lemmy and Kbin do federate with each other. You can follow Lemmy "communities" in Kbin, and Kbin "magazines" in Lemmy, and I believe other Fediverse groups (like Frendica groups) also federate.
I've been leaning into this from Kbin, as a way of dipping into communities on Beehaw and other Lemmy instances while keeping my distance from Lemmy's devs.
I have one concern. As we're seeing with Reddit, it's a huge effort to move internet communities. If Lemmy-the-app becomes untenable even for more reasonably admin'd instances, then the most obvious solution won't be to fork Lemmy (a huge undertaking) but rather to move to an app that's maintained by more reasonable people. That's probably going to involve a messy migration, some data loss, some loss of community, and some dead links.
I'll keep using Kbin as a way of tapping into existing communities, but when it comes to building new ones I'd much rather see it done on kbin.social or other Fediverse instances where there's no long-term dependency on Lemmy's devs.