Yes; but if they want to release the BSD kernel as a whole under the FreeBSD license, then they already cannot incorporate code that has any other license whatsoever. For example, they wouldn't accept my patch under the hypothetical license "you can do whatever you want with this code except shoot bunnies". If they did, FreeBSD users couldn't use FreeBSD to shoot bunnies.
Am I missing something about the BSD kernel licensing social dynamic?