I NetApp is suing Sun for patent infringement over ZFS. DTrace can be turned off - a file system, not so easily.
So that is exactly backwards as to who is asking for indemnification. Apple would be asking Sun to cover any awards to NetApp.
Until the dust settles on that, Apple probably doesn't want to put 10-20 million copies of something out there that has a significant chance of loosing in a patent battle. If that turned out to be $10-20 a copy penalty for the violation that is a big chunk of money.
Furthermore, because Sun is in limbo there is probably no one at Sun right now who could sign Sun for such a huge liability. Selling yourself to another company and that taking on a huge liability in the middle of the long transaction usually leads to trouble (get sued and/or costs more money) or at the very least political suicide (tagged as someone who saddles company with risks... not going to make the "keeper" list on the merger process.) .
Even if was in the direction you stated. Sun wanted indemnification for changes Apple made to ZFS to jam it into OS X that for some reason Sun was going to merge back into the core ZFS code tree.
There are also technical issues you are sweeping under the rug.
ZFS changes the why the kernel goes about dealing with the "file system". It isn't a file system. It is a volume manager merged with a file system. That is anti-Linux design philosophy. No way Linus would vote thumbs up on this even if it had GPL license on it.
[ Besides Oracle "liked" Linux in part because it didn't have an operating system. Now that they have Solaris ... it is dubious to "give away" one of the crown jewels of Solaris , ZFS, to Linux. Putting people on Solaris is a better opportunity for Oracle to make money than on Linux. In selling support contracts for OpenSolaris ( or the non open version) Oracle is the #1 player. In Linux, they are much smaller player to Redhat.
Besides when has Oracle taken a software product and slapped a GPL licesnse on it. There was stuff that was already GPL. Or defacto had to be GPL'd (core Linux additions). But name something that Oracle has injected into the GPL space when didn't "have to" ?
The GPL was/is useful in reducing the price of largely, historically, complementary offerings. If people pay less for OS and server hardware can pay MORE for Oracle stuff. Reduction of cost of complements.
Now that they will be in the OS and hardware game. Why accelerate knocking down complements?
Even more so in that Solaris/ZFS is a
critical enabler of Suns universal storage devices. Those bring in
cold hard cash money. When the last time you saw Oracle walk away from cash money?????????????
]
Likewise squeezing this into Mac OS kernel would have issues both in user experience ( people just unplugging disks ) and in weaving those mods in with all of the other Snow Leopard updates in flight.
ZFS made much more sense when Apple still had XRaid and might have been inclined to expand past just 1U servers. Backtracking on XRaid. Having XSan , Time Machine success (in the consumer space), and barely treading water on servers ..... the biggest 'bang for the buck" for ZFS is not there; especially in the short term.