Well, if you think about it, is is actually the same as putting water at a window. The moonlight falls on the cloud(=vaporized water) just how it would fall on a bowl of water. So, I perosnally think that it WILL be moon water, but less potent than moon water obtained through the bowl method because of...well, physics. A cloud is not compromised only of water vapors, but from other gases as well. This means that moonlight, due to not being equally absorbed by every part of the cloud, doesn't affect water on the same level it would if the water was inside a bowl with nothing else but water.
In a nutshell: you CAN get moon water through this method, but it will be certainly less potent than obtaining it with the classic way.