Is going for refuge central to all Buddhist traditions?
In every single branch of Buddhism I have looked into, going for refuge is seen as the defining feature of what makes you a Buddhist. The Theravada school holds to this position, every form of East Asian Mahayana Buddhism I've read about holds this position, and Tibetan Buddhism also puts great stress on going for refuge to the point where reciting the refuge formula with Bodhichitta 100,000 times (usually combined with prostration and visualizing the refuge tree) is a central part of Tibetan Ngöndro, or foundational practice.

I think that Sangharakshita really was correct in identifying the central role of refuge in all Buddhist traditions.