Command line equivalent of Disk Utility, which is not diskutil, to obtain UUID
Update:

IOReg gives the partition UUID, not the volume UUID, as it operates below the HFS layer. I had incorrectly assumed that the device UUID was required rather than the volume UUID because it was substituting for a device node. To get the volume UUID, use hfs.util. For example:

/System/Library/Filesystems/hfs.fs/Contents/Resources/hfs.util -k disk0s3


Replace "disk0s3" with whatever the "device identifier" of your volume. This is different to the "device node" (which is "/dev/disk0s3" in this case").

Original IOReg details:

You can run ioreg -c IOMedia -r to show the device tree for the disk devices in your system. This should give a manageable amount of output (as compared to ioreg -l, which shows everything).

If you want to just extract UUIDs, you can ioreg -c IOMedia -r | grep UUID, but the downside is that you lose context.

The diskutil information is interesting; it obviously depends on daemons that do not run in single user mode.