Custom fields added to an incident impact statement are not picked up by the Fivetran connector currently, I believe this is due to that data being exposed by a different endpoint than the overall incident endpoint. example endpoint below: 

https://api.datadoghq.com/api/v2/incidents/{incident_id}/impacts

sample of the fields object returning: 

"fields": {
                    "service": "my-service-name-here"
                },

We use Services attached to an impact statement to clearly define the nature of the impact to each service/application, bringing this data into Snowflake would allow us to better visualize these impact statements over time.