We have a lot of cross-pollination between Linux and the BSDs, the people developing for each
O.S. can read the other's source code just fine.
Granted, you can't always re-use the code itself, but that *really* isn't what matters most,
especially for drivers. In fact, it is best if things remain as they are. We get better code
quality and a much higher degree of freedom to change interfaces that way.
The really precious information (how to talk to the hardware) is already shareable among all
since the code is open anyway. That's the only thing that matters.