No the reason for 2 hoses is to maintain the pressure in the room. So you bring in outdoor air to run over the unchilled liquid to cool it down and then that becomes hot air and you exhaust it back out. Then when the liquid is cold, you bring in air from the room, cool it and spit it back in the room.
If you only have one hose, it draws air in from the room to cool the liquid and then exhausts that air outside. You now have a negative pressure (like having too many "out" fans on your computer) and air will come into the room from any gap it can find, so you're going to be bringing warm air into the room as a result. I don't know how well documented this effect is, but I've heard anywhere from a 25-50% loss in efficiency.