Can I use a swamp cooler to cool an AC unit's condenser?
Using a water cooled condensing units for refrigeration is not a new idea - large chiller units have been doing this for many years, but it's not as simple as hooking up a hose and letting er rip...  there's a lot of additional maintenance involved with all the cooling water infrastructure - even a simple spray evaporation cooling system requires nozzle cleanings, pump maintenance and such pretty regularly.

Home AC units don't really need the efficiency boost from evaporative cooling because the air cooled condensing unit(s) are efficient enough without introducing the complexities of water lines, spray bars and a drainage system for a small direct expansion system.  If the condenser is not giving you the proper heat rejection - just upsize the heat exchanger... far cheaper and more reliable right?

That being said, I have a window unit AC that takes the condensate and splashes it back on the condenser fins to boost efficiency, and I know there is a model of RV air conditioner which does the same thing.  It is possible this feature has been added to DX condensing units - but I have been out of the HVAC world for some years now.