There are 10 criteria for meat being certified as Certified Angus Beef. All 10 criteria are inspected on the carcass. The inspectors don't ever see the cattle on hoof. A Polled Hereford can end up in your store as Certified Angus Beef.
It would have made more sense to just add another ‘grade’ to beef, rather than using a breed name. Call it extra-prime or something like that.
In my opinion a Holstein/Hereford cross is about the best beef you can get if it is raised right.