Yes, they work. It's a united flight operated by an Aer Lingus aircraft and crew. The gate agents are all UA, the ground guys are UA. You can even look up the flight on expressnet. There is even a thread on here from a guy who took a ride on the outsourced aircraft and snapped a picture of the UA mixed with Aer Lingus seat pocket stuffs.
I also know an FA who sent her daughter to Madrid on the flight.