Fakeroot was designed to confuse tar (and cpio) into believing all files are owned by root.
So the default setting for fakeroot will work perfectly if there are only files (directories and links) and they should be owned by root. If some have to be owned by "tc" or "staff" things may break without save files. (Note: The chroot() system call and secure device access won't work; eg syslinux/grub)
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Looking at core.gz it seems to have device files built in, so you're not completely wrong.
Fakeroot needs a save file to preserve those.