Use NestedStack to use the type

monitor_nested.ts

import * as cdk from '@aws-cdk/core';
import {CfnResource} from "@aws-cdk/core";

export class CdkCustomResourcesStack extends cdk.Stack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const monitorType = new CfnResource(this, 'datadog_monitor_id',{
      type: 'AWS::CloudFormation::ResourceVersion',
      properties:{
        'TypeName': 'Datadog::Monitors::Monitor',
        'SchemaHandlerPackage':
            's3://datadog-cloudformation-resources/datadog-monitors-monitor/datadog' +
            '-monitors-monitor-2.1.0.zip'
      }
    })

    const monitors = new DatadogMonitor(this, "test_monitor" )
    monitors.node.addDependency(monitorType)
  }
}


export class DatadogMonitor extends cdk.NestedStack {
  constructor(scope: cdk.Construct, id: string, props?: cdk.NestedStackProps) {
    super(scope, id, props);

    new CfnResource(this, "test_id", {
      type: 'Datadog::Monitors::Monitor',
      properties:{
        'Type': 'query alert',
        'Query': '<YOUR QUERY>',
        'Name': 'Test monitor',
        'DatadogCredentials': {
          'ApplicationKey': '<YOUR APPLICATION KEY>',
          'ApiKey': '<YOUR API KEY>',
          'ApiURL': 'https://api.datadoghq.com'
        }
      }
    })
  }
}