Thanks for the posting your "diskutil list" output; it enabled me to tailor this command for your fusion drive.
I gave it a shot and didn't get any dire warnings, but neither did I get any action. When it asked for password, I entered my login password and got this response:
Last login: Tue May 14 18:17:00 on ttys000
iMac:~ myname$ sudo dd if=/dev/rdisk1 of=/dev/null conv=noerror bs=1024000
Password:
dd: /dev/rdisk1: Operation not permitted
iMac:~ myname$
