When /usr/share/initramfs-tools/scripts/init-bottom/0_kdump is run, only the root partition has been mounted. Since it needs to read /boot/vmcoreinfo-$KVER, run /usr/bin/makedumpfile, and write /var/crash/vmcore and /var/crash/vmcore.log, it will fail if any of those files are on separate partitions.
In the /boot or /usr case, it will actually fail in such a way as to cause the rest of the system to continue booting inside the crash kernel (bug 600051)!
Binary package hint: kexec-tools
When /usr/share/ initramfs- tools/scripts/ init-bottom/ 0_kdump is run, only the root partition has been mounted. Since it needs to read /boot/vmcoreinf o-$KVER, run /usr/bin/ makedumpfile, and write /var/crash/vmcore and /var/crash/ vmcore. log, it will fail if any of those files are on separate partitions.
In the /boot or /usr case, it will actually fail in such a way as to cause the rest of the system to continue booting inside the crash kernel (bug 600051)!