Yes CX has the power to Veto any airline wishing to join as they are a founding member of the alliance. So that means it is likely any bid for CZ to join Oneworld would need to benefit CX (which I don't know how CZ joining in anyway can) and if not then they will likely deny them entry. AA would prefer them to become a full member but realistically CZ won't join an alliance for many years if at all. Skyteam was and is still the best fit for them from an alliance point of view. But exiting that alliance will free them to codeshare and JV with many more airlines (Especially AA) which they think is a better path for them.