I have not attempted this with a cloud folder, but have done this successfully with local folders.
I don't see why that would not work using a cloud folder. The key is, the entire iTunes directory would need to be in the cloud folder, the .itl and .xml files as well as .itdb are the keys to identifying the contents of the media library, and enable iOS devices to sync to any Mac (or PC) that the device connects to.
But, a few considerations before going down this path. First, do all computers (and your cloud service) have enough space to store the full media library? The cloud services will replicate the files to all of your computers, and store a copy in the cloud.
And second, is the media library organized. I have all of my music on my default /Users/username/Music/iTunes location, but Movies are on a separate USB drive (I have 1.5TB of movies ripped from DVDs). The iTunes database contains links to media file locations in the form of a path. So, that path would need to be consistent on all computers for this to work. In my case, the /Volumes/USBDriveName/Movies would need to be consistent on all of my computers. Further, this alternate Movie location would also need to replicate across computers via the cloud service, else attempting to play content that is not accessible on the other computer would return the dreaded media not found error.
Assuming you library is consolidated in the default location and all media is contained in the iTunes folder, just move the entire iTunes folder to the new location. Do this with iTunes not running on any of your computers. Once sync completes replicating the entire contents to all of your computers, then you are ready to set iTunes to use the cloud folder.
A good way to do this is to launch iTunes while holding the Option (Mac), or Shift (PC) key. This informs iTunes to prompt you to create or select an iTunes library you want to open. Simply select the iTunes library in your Cloud path, and you should be good to go. Any updates on one computer should replicate to all, but I suspect you would need to get in the habit of shutting down iTunes when not in use so that file replication won't run into conflicts with open files on the other computers.
To be safe, you might want to test this by creating a new iTunes Library in a cloud folder and place just a few songs in it. Start by using the Option or Shift when opening iTunes on one of your computers, choose the Create Library option when prompted, and select a cloud folder, add a few songs, synch an iOS device to the new library, then close iTunes. Then, on another computer, use the option\shift method to choose the new library in the cloud folder. If you see the songs you created in the new library, and can sync your iOS device to it, then you know this will work for the entire library.