Terraformer datadog provider hasn't been updated in 3 years:
https://github.com/GoogleCloudPlatform/terraformer/tree/master/providers/datadog
I recommend using Dogmover's successor, github.com/DataDog/datadog-sync-cli, for this purpose.
# Import resources from parent organization and store them locally
$ datadog-sync import \
--source-api-key="..." \
--source-app-key="..." \
--source-api-url="https://api.datadoghq.com"