From what I have read, and I assume it is is largely accurate, these drivers are badly paid and pretty badly treated.
If it is correct that around 90% of the workforce are from an ethnic minority, it seems to me that the company could be open to allegations of exploitation. I don't think the phrase "playing the race card" is particularly acceptable in any circumstance but especially not when it is used in this situation where the company is responsible for vetting employees and setting out terms of working.
It is not, in my opinion, acceptable to employ possibly unfit, unsuitable and unsafe people or underpay and mistreat employees in order to achieve rock bottom prices
in order to seriously undercut any competitors in order to gain control of the market.
To say that if Uber is closed down these drivers will have no work is not a reason for continuing with bad and possibly unsafe practices. Using that argument, the flouting of any sort of health and safety regulations could be justified on the grounds that "at least they've got a job".