Can agents submit requests from the Help Center using the Submit a Request button?
No, this is not natively possible at this time. Help Center only sees four roles: manager, agent, end user, and anonymous. And only anonymous and end users roles are able to access the submit a request form. See our Help Center roles and permissions.
This is a hardset system rule and there isn't any method to overwrite it at the moment. There is a related discussion about this functionality in our Product Feedback forum: Add Submit a Request for Agents.