Its probably a joint venture between the two. Uber bring the client booking system, and Volvo bring the vehicles. I'm sure Volvo has more ownership too.It's gonna be a free for all once every major manufacturer has a working model.
What I want to know is how the partnership breakdown will work- Volvo won't simply relinquish control of an entire fleet to Uber (or yellow cab) for peanuts, they will want to get market price for their vehicles (whatever the MSRP is).
Also, Uber has never owned a single vehicle.
They have no idea what maintenance and insurance of a 24 hour robotic fleet is going to cost.