The S-5 PVKIT / S-5! standing seam clamp assembly is a UL2703 listed bonding device. While the listing covers carrying a ground path from PV panel to PV panel, the clamp to the roof panel material is not included in this certification.
On an individual basis, some independent racking companies have worked with certification labs to verify the clamp-to-roof connection and its reliability as a bonding path. For instance, IronRidge has found that S-5! clamps provide a reliable bond path between the clamps and the roofing panels beneath the array. This rating is included in their racking systems UL2703 listing.
Please see page 4 of the links:
Grounding path as concerns module-level-power electronics (MLPE): If the microinverter does not have internal grounding, then it will need to be independently grounded when fixed to the roof. If the microinverter is fixed to the module frame, then it can be grounded via the module frame.