Corrupt GPT on ZFS full-disks that shouldn't be using GPT

[Quartz]

>Do I need to export the pool before using dd on the
> raw device?

So I think my earlier comment saying export is overkill might have been 
wrong. The handbook page explaining how zfs checksums work has an 
example that explicitly uses export:

[20.3.8. Self-Healing] "Data corruption is simulated by writing random 
data to the beginning of one of the disks in the mirror. To prevent ZFS 
from healing the data as soon as it is detected, the pool is exported 
before the corruption and imported again afterwards."

https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/zfs-zpool.html