Does the email address assigned to the API user need to be an email address maintained by an actual person?
The email address assigned to an API user does not need to be an existing email address or an actual person.
It is used as an identifier for the API user. Generally, customers name the API user according to the integration the API user is being used for (e.g. firstname.lastname@example.org). This is useful for tracking where API calls are coming from when there are multiple integrations configured with Marketo via the API