[pandaman]

>I'm honestly curious how CloudFlare will handle reference checks for these people

Just like every other company: confirm the start date, the end date, and the job title. Nobody in their sane mind will give anything else.

[FireBeyond]

I'd say that a very large portion of companies also ask, and answer, the question, "Is the person eligible for re-hire?"

[gitfan86]

Background checks only confirm information given as part of an application. Employment and job title.

References however can be more about the quality of the work including "would you work with this person again?"

HR only does the background check part. The job of an HR department is to make the company look good. They do not want to start a conversation about how they hire bad employees or initiate a conversation where the former employer will tell their side of the story.