In https://github.com/mongodb-labs/drivers-evergreen-tools/blob/master/.evergreen/ocsp/ocsp_mock.py the multi-word arguments are defined using underscores to separate words:

 parser.add_argument('--ocsp_responder_key', type=str, required=True, help="OCSP Responder Keyfile")

The convention for multi-word arguments is to separate the words with dashes:

--ocsp-responder-key

Unless there is a strong reason to deviate from the convention, the tools should use dashes to separate the words.