As a followup, here are the responses I got:
From Gigabyte:
Answer : Dear Customer,
It will not work as it will causes for it to short, it cannot be in any contact with the bottom of the case.
From CoolerMaster:
Hi Mr. Adams,
That is normal. The backplate has anti grounding tape on both sides. If you have any other questions, please let us know.
Respectfully,
Marvin Ruelas
Support Specialist
Cooler Master USA, Inc.
1-888-624-5099
4820 Schaefer Ave
Chino, CA 91710
I still feel better having carved out the back.