If there is Unix IP in Linux, the owner, whomever it is, could charge a fee. The reason that wouldn't make a lot of sense (unless the fee is very small) is that it would make it less competative and that would hand Microsoft a more dominant position. If you want to consider plots or conspiracy theories, consider the payback that buying and releasing the Unix IP to Linux would yield after the Microsoft and OS/2 fiasco. IBM has no love for Microsoft (not only because of OS/2 but also because of Microsoft's strong-arm licensing agreements that IBM didn't really want to agree to).
consider the payback that buying and releasing the Unix IP to Linux would yield after the Microsoft and OS/2 fiasco. There is a potential payback, but only if IBM can help correct other Linux ailments such as lack of indemnity. Linux definitely has potential, but it remains a diamond in the rough that needs to be further polished which will continue to require signficant investment.
Unix on the other hand, is a Cash Cow in waiting (via other Unix income) ready to bear tremendous milk if the Linux users have to finally fork over some money for their wares.
I'd say it would be a tough call, but back to the SEC, I don't think they would allow the buyout unless IBM takes over rights and continues to charge for them, simply because IBM is the accused. Just a guess of course.