There's no "QA person" as you may imagine. I'd say it's mostly done by the product team behind the service.
Thanks for the question!
ServicesDB indeed integrates with a lot of external tools like Pingdom, PagerDuty and Bugsnag, but in general it's not something that each team can choose. I imagine that it's for the best of everyone at the company that, for instance, all on-call management is done in the same service (PagerDuty).
I'd recommend you to watch this a talk about ServicesDB, as it uncovers more details: https://www.youtube.com/watch?v=KvySt3yt5vs