In fact, nobody guarantees that say Fedora will run on an Ubuntu-built kernel. Or even on a kernel from a different version of Fedora. So, IMO, anything other than running the exact same OS on host and in container is a hack.
"nobody guarantees" just means that you can't externalize the work of trying it and seeing if it works. I don't think that's a huge loss, considering the space of all possible kernels, configuration switches, patches and distro packages is huge.
It's like refusing to use a hammer because nobody can assure you that hammer A was thoroughly tested with nail type B.
As long as the ABI is stable and you don't reach out to something that would have moved within /{proc,sys,whatevs}, you're good. [0]