Well, the plants will produce oxigen on their own, and your room will not be 100% air tight so you will still have fresh air seeping in, and as little as it may seem, there will still be enough for your plants. The main thing is to be able to have good air circulation with in the room, fans which are moving that air in the room to help strengthen the plants and provide the needed air movement for your plants to expire and absorb CO2, O2 water and so on. This all being the case, you do not need to duct the AC out of the room, just get the kind that can recirculate air without needing to be venting outside air in.
Is this going to be a grow using CO2? If not, you can bring in all the fresh air you want, the reason most people use a sealed room is to improve yields by using CO2 and venting in fresh air would defeat the purpose because it would disapate the CO2 unless you had a fairly complex venting system that stopped air coming in during the CO2 treatments, but if you can control all the temps without having to vent from out side then you are going to have less hastle. Also, with those aircooled hoods, they have to be air tight, so that when the air is being pushed, or pulled outside it is not sucking any air out of the grow room, or it will take the smell with it, and the CO2 as well.
Adieu