monitor AWS rds dBInstanceStatus

Typically you can provide a status of a service/device by using the dashboard NOC widget. That does rely on LM alerting to report on a problem with the RDS instance, but likely the easiest, universal way.

Otherwise you might need to create a custom DataSource (or modify AWS_RDS) using custom CloudWatch metric (if that is available) with the Cloud Collector. Or use a local Collector and code a DataSource that queries AWS directly to provide the data as a DataPoint.