If these 'hackers' were white hat and signed a contract saying they responsibly handled and deleted the data, and then uber checked the access logs of the data and verified that nobody else accessed it, then IMO it is not a data breach. It was a potential breach.

A white hat hacker you have an agreement with on how the data should be handled is the same as an employee who has access to the same data, where you also have an agreement on the employees use of the data.

You might say "Ooh, but can you trust the hacker not to keep a copy of the data!?!", but it's exactly the same as saying "Can you trust the employee not to copy the data?". I don't think a company would announce a data breach just because the database administrator had access to a backup tape...