Your issue will be the bootloader. In this thread, an A9 partition is created and formated with the FFSv2 file system:
A special grub2 entry had to be created to boot the NetBSD / partition.
https://daemonforums.org/showthread.php?t=11898
To my knowledge, NetBSD's default amd64 bootloader will not allow you to boot non-NetBSD partitions.