In short, no. The backup generators are engine driven, 'frequency wild', thus rely on engines operating in order to work.
If you lose both engines, the ram-air turbine will automatically deploy.
It will provide hydraulics to the essentials first, and if it has spare capacity, will provide electrical power to the Captains flight instruments, and through another bus, the FO flight instruments.
There is a delay in receiving electrical power, however. All screens will blank, the RAT will get to work, and a minute or so later, some electrics will be restored as per above.
Hope this helps..