They definitely are. When I take Uber/Lyft I notice that most drivers are running both apps. As they get towards my destination they will start bobbing for fares between the two apps. Maybe Uber is paying slightly more for drivers? I don't know, but maybe that is why they tend to favor Uber rides over Lyft. Maybe they are more likely to get tips on Uber. Just some theories. But I have noticed the same thing, most drivers tend to favor Uber. So if they gets rides from both, they will cancel the Lyft one.
I used to switch between the apps based on price of rides. Now I have AMEX rewards for Uber plus I get Marriott points when I ride, so that is why I have moved exclusively to Uber.
But the drivers are the same. It's the same pool of drivers, using both apps.