We have a lot of the "silliest" answers here, from people who have no datacenter or AC experience. You put up a bounty, you get stupid spammers and beggars.
Inside a closed air conditioned building, evaporative cooling may enhance efficiency a bit. AC removes humidity, to the point where the IDUs need to pump water out. You could add some humidity back to pre-cool the hot AC intake air (you can't humidify cold air AC output). The humidity would have to be strictly monitored to not go overboard or add more humidity than the AC can remove.
+1
You should pass some of the bounty to DC for being so accurate and on point.
If you are doing raised flooring, you will have moisture sensors under the floor (spills, leaks, plumbing, flooding), you may also want air humidity alarming if you are using swamp cooling as part of your mix.
Design for what happens when things go wrong, not just for how you want it to work.