Licences being incompatible is a moot, philosophical matter (least until the *AA succeed in
making copyright infringment a criminal matter) if no one thinks the infringment matters. Who
exactly is going to sue if someone distributes a DTrace modified kernel? Sun would have no
standing, as the CDDL seems to allow combining with GPL works.
So it'd have to be a Linux kernel contributor, sueing someone for distributing free software
derived from free software.