Yes, my company uses Tusker and they offer a "premium independent servicing" option for EVs which saves a few £/mo. Can't be that hard to do considering even Kwik Fit and Halfords offer "dealer equivalent servicing" that guarantees to keep to the car's warranty conditions.Early days yet for EVs but we used to use Tusker for our fleet and they used their own 3rd party partner for maintenance and it was cheaper for them and for us than dealer. As a driver they took care of bookings and relief cars.
They had an agreement with the 3rd party to use original parts and to keep a journal of service actions and parts used to be sold with the car to ensure they could legitimately say the balance of the manufacturer warranty was there even with the 3rd party economies.
I suspect this will happen with EVs too as the volume grows.