Ideally your DR and emergency response systems should be not hosted on your infra and have circular dependencies . i.e.Amazon should not be hosting status page assets on S3 as they were.

At the very least they should be hosted isolated of your production service components at all layers, so both don't go down at the same time.

For slack my guess is their internal slack is not hosted on slack prod and hopefully also does not share components below L4 as well ( DNS, IP , domain, routing etc )