This situation seems to be more analogous to an out-of-tree driver which reaches into kernel internals, which Linux does break all the time.

if the out-of-tree driver does not touch kernel space, it should not be broken.

Well yes, if the out-of-tree driver sticks to public stable APIs it shouldn't be broken. And analogously here, if the software in question stuck to public stable APIs and didn't reach into private internals it shouldn't have broken.