I don’t think it’s advisable to run both at once. Maybe if your cooling system was set up so the AC was cooling the pre-cooled air from the evap cooler? Perhaps then you could achieve lower temps with a little less energy, but it would likely take a lot of management. Evap coolers don’t operate like ACs, which recirculate indoor air over chilled coils. Instead, evap coolers are pushing dry, outdoor air through a wet membrane and into the house. So you actually need to leave a window open so the chilled air can move into the house and replace the warm air. If I was to run them both, I’d first crack some windows and then run the cooler. Once the house was as cold as possible, I’d then close the windows, turn off the cooler, and turn on the AC. You wouldn’t really be controlling the humidity because the AC would just remove what water the evap cooler added to the air.