Blue Coat currently doesn’t have support to monitor the DRTR service using SNMP. The only way of doing this is using the exposed URL to test the status of a health-check:
https://<sg-ip>:8082/health_check/test?<health_check_name>
This URL will respond with a 200 HTTP response code if the health-check is successful or a 404 if the health-check is down.