Can I set a scorecard rule to monitor Datadog monitors/SLOs based on tags?

Yes! You can specify key-value pairs that allow Cortex to auto-discover your SLOs and Monitors and use these tags in Scorecard Rules:

x-cortex-apm:
  datadog:
    serviceTags:# List of tags & values
      - tag: <key>
        value: <value>

You can read more in our Datadog integration docs.