Connecting to a different machine via Firewire is not seen as an owned drive.
Furthermore, the actual file directory on the volume is no different in either OS. They're both HFS+ filesystems and the directory is the same. That's why you can see the files on a target disk from a different machine… you're reading the existing directory.
Connecting to a machine in Target Disk mode does not write a "special" OSX directory on the target or even a "OSX was here" message.
It is assumed the drive is temporary because it's in a different machine with a different MAP address.
Since I have the 667MHz PowerBook G4 on the table with the top cover off, which makes swapping mSATA drives on an adapter a breeze, lets conduct the two tests.
1. Moving "virgin", empty external FW drive from OS9 to modern-ish OSX (Yosemite) and back.
2. Connecting PB G4 with "virgin", empty, OS9 initialized internal drive in Target Mode to MBP2011 running Yosemite and examining the same drive in OS9 afterwards.
* Both tests produced the same result, I will report only on latter.
At first, to clear it upfront:
* Spotlight is completely yanked from all my OSX machines. Parts of it are deleted, remaining Agents and Deamons disabled and unloaded. (I use different search tool in place of it).
* Many other Agents and Deamons are also disabled and unloaded with the help of LaunchControl.app
* I've never ever used Time Machine. It is deactivated. (CCC is the tool for the job).
The test.
1. Mount mSATA drive on mSATA->SATA adapter, plug it into Freecom external FW dock and connect it to OSX machine.
2. Write all zeroes to first ~30MB on the drive with the help of iBored app to make sure that no remains of any kind of partition table etc. from any OS are left on the drive and that it will appear as "unformatted" to any OS.
3. Mount the unformatted mSATA drive on mSATA->ATA 44 adapter inside the PB G4.
4. Plug another, OS9 bootable 2.5" SATA drive into external FW dock, power up the PB G4 and boot from that external FW drive.
5. In OS9 initialize the PB G4's internal drive on ATA bus with Drive Setup 1.9.2.
6. Done!
In OS9.2.2 the drive is shown as empty (0 items), but lets examine the invisible files with Norton's Fast Find, prior to allowing the OSX to see this drive.
OK, nothing unusual here.
Shut down the PB G4, power it up in Target Mode and connect it using FireWire to MBP2011 running Yosemite.
Lets check what the Disk Utility sees. Yes, everything looks normal. All those partitions are various OS9 ATA/SCSI/FW drivers.
Now, lets take a look at invisible files on the same drive with OSX tools. Whaaaat? What's that? Some of that stuff wasn't there when we checked the invisible files in OS9 in prior step.
OK, lets boot the PB G4 back to OS9 and check the invisible files again. Bang! A couple of new items.
Now, if we try to run DiskWarrior, we get this.
What about Norton Disk Doctor?
Norton sometimes succeeds with the repairs, sometimes not, but, in any case, DiskWarrior will always say that the drive is damaged.
Draw you own conclusions.
EDIT.
DiskWarrior 2.1 is not compatible with disks that have Mac OS X 10.4 (Tiger) or later installed.
It is also not compatible with any disk that has been attached to a Mac running Mac OS X 10.4 or later.
https://www.alsoft.com/support-diskwarrior-21-earlier----
https://techblog.willshouse.com/2011/05/05/what-is-fseventsd/https://arstechnica.com/gadgets/2007/10/mac-os-x-10-5/7/