@Mattias P :
Unfortunately, it is not currently possible to manage access to the Hive Metastore catalog (or other external metastores) using the databricks_grant resource in Terraform. This is because the databricks_grant resource is specifically designed to manage access to Databricks resources within the Databricks workspace, and external metastores are not within the workspace.
However, you may be able to manage access to the Hive Metastore catalog using a different method, such as creating custom roles and permissions in your Hive Metastore service, or using a separate tool to manage access to the metastore.
Alternatively, you could consider using Databricks as the metastore for Rudderstack instead of using an external metastore. This would allow you to continue using the databricks_grant resource in Terraform to manage access to the Rudderstack integration in Databricks.