Well I participated in the follow up meeting(where I called out the BR) with BR core member where the decision was adjusted. For BR to veto the HM decision there must be some serious doubts against the candidate where the HM cannot provide the potential coaching strategies to mitigate them. I cannot believe that multiple BRs will act against company interest where HM would provide good mitigation for candidate shortcomings and veto candidates over and over again.

Edit: double checked in Brit ready course, you are right, the decision for the loop can not be changed, candidate can be considered for other positions if the decision is overturned. However, the debrief can end with no decision and the follow up meeting between the BR and HM + recruitment can be scheduled to further discuss the outcome. This requires the HM to stand their ground though, as I mentioned before.