Usually I hear it in the context of a person outside the team added to an interview panel, to help ensure that the hiring team is adhering to company-wide hiring standards, not the team's own standards, where they may differ.

But in this case I'm guessing their incident analysis teams also get an unrelated person added to them, in order to have an outside perspective? Seems confusing to overload the term like that, if that's the case.

Bar raisers for COE are those who review the document for detail, resolution, detailed root cause and a clear set of action items to prioritize which will eliminate or reduce chance or reoccurrence.

It’s a person with experience.