What role is needed by the MID Server's user account to interact with a ServiceNow...

 The MID Server’s user account must have the mid_server role to interact with a ServiceNow instance. This role allows the MID Server to access protected tables and perform discovery and orchestration tasks on behalf of the instance. The other roles are not related to the MID Server functionality. The discovery_admin role is for configuring and managing discovery, the sm_mid role is for using the Service Mapping MID Server, and the mid_discovery role is for running discovery probes and sensors.

References:

Setting up MID Server user and role

Configure Windows MID Server service credentials

Correcting MID Server Windows service account user and permissions