Sure, but Uber previously styled themselves as just a middleman between drivers and passengers - the facilitators of a market, not a force in the market of their own.
Consider a counterexample - eBay is clearly a market. Independent buyers and sellers agree to transactions, on their own terms. eBay competes for the attention of both buyers and sellers, in terms of service and fees, not on the prices of the actual goods in the market.
If the competition that's happening in the transportation market is between Uber and Lyft, and that competition is on the price of rides and quality of rides, then Uber isn't a market, it's a vendor in a market - and thus the drivers aren't vendors within Uber's market, they're just employees of Uber.
Consider a counterexample - eBay is clearly a market. Independent buyers and sellers agree to transactions, on their own terms. eBay competes for the attention of both buyers and sellers, in terms of service and fees, not on the prices of the actual goods in the market.
If the competition that's happening in the transportation market is between Uber and Lyft, and that competition is on the price of rides and quality of rides, then Uber isn't a market, it's a vendor in a market - and thus the drivers aren't vendors within Uber's market, they're just employees of Uber.