The DIAMONDBACK™ flexible gas piping or other gas system components shall not be used as a grounding electrode or as the grounding path for appliances or electrical systems.

This quote from Diamondback brand CSST appears to support that the fireplace should not be bonded THROUGH the gas line.
If the fireplace is electrically connected to a three wire system, that may suffice, but I would really like to hear some more knowledgable veiwpoints.

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Jim Luttrall
Mr. Inspector.net, Inc.
Allen, Texas 75002