Here's my anecdata. Every Uber/Lyft I've taken is clearly servicing both. Indicators range from multiple phones, one with each app running and multiple logos/stickers on the cars. I almost always ask the driver which they prefer. The consistent answer is they prefer working with Lyft better but Uber more consistently has rides for them to pick up. It's unclear whether they get paid better with Lyft or are otherwise treated better, but that is what they say every time.