@aaron Thanks for reporting this. Nice find. There have also been reports of unetbootin also producing non working Rockstor install usb keys. I have added you contribution to the docs issue on this matter. That way we can hopefully help others avoid this same issue.
Cheers.
I use the following myself (with the proper usb device specified of course):-
N.B. use with care as it will happily overwrite anything on the specified device.
sudo ddrescue -d -D --force Rockstor-3.8-9.iso /dev/sdx
There is some related discussion re usb creation over on another forum thread, might be worth a look.