Earlier quoted context omitted.
both zfs and nvidia do it, don't they? Or at least they haven't been in trouble over it :)
Korg ships a module with their Kronos workstation that re-exports some GPL symbols as non-GPL. They also ship the source for the kernel itself, but "conveniently" forgot to include a patch they added for DRM that makes their synthesizer module (yes the synth runs in kernel space) fail to work properly if missing. Some obfuscated change to the CD-ROM subsystem (yes really, they stuck some unrelated protection in there…
Wouldn't it just be better to reimplement whatever functionality they require themselves without recurring to GPL modules that break the license and expose them to legal risk?