I'm not an expert but the UCI document labels it as "1 main camera, 1 opposite". So I would guess the "main" camera is the source of truth and the other is a backup?

Either way, presumably both cameras ideally need to be aligned to the line as stated. That should be possible and perfect alignment between the two cameras isn't required. I can't see anywhere that it states the two cameras actually need to agree, isn't it fine providing one of them is used consistently.