Hello,
This forum is about Orthanc, not about the products by Google.
If you are confused with Google Cloud Platform's documentation, please contact the professional support from Google: You pay them to this end.
The Orthanc plugin contacts Google Cloud Platform as a DICOMweb client (i.e. over HTTPS), there's no DIMSE protocol into play here. The plugin only manages the authentication keys for DICOMweb requests:
Sébastien-