If you are using SMART Playlists, there is a constraint: For you to see the songs in a SMART PLAYLIST on your iOS device, you must first have them already locally on the device.
This is a chicken and the egg situation, in my opinion. The only work around I have found is to do this:
1) Create a NEW PLAYLIST using File, new Playlist. Name it "SMART CLONE" (for purposes of this example)
2) Go to the Smart Playlist you want to have on your iOS device and select edit, select all.
3) Drag and stop all tracks selected to the "SMART CLONE" playlist.
4) Launch MUSIC on your iOS device and give it about 30 seconds to 10 minutes for the "SMART CLONE" playlist to syncrhonize the informational track references/names.
5) Click DOWNLOAD ALL at the bottom of the "SMART CLONE" playlist.
This obviously ***** because 1) it takes away from the "automation" smart playlists bring to the table, and 2) requires access to your computer to implement the work around. So if you forgot to do this before leaving house, you cant just use the Smart Playlist.
The troubling information I took back to Apple Support was this: I created the regular playlist, dropped all the tracks from the smart playlist, saw the tracks on the regular playlist, downloaded all. I then went to look at my smart playlist on my iOS devices and even though the files are now local, they still dont shop up in the smart playlist. So their explanation does not really seem to be the problem.
Further, I have 2 Apple TVs. They both have Home Sharing and iCloud enabled. The Smart Playlists show up as fully populated in both views/modes. So they are obviously going from iTunes to iCloud entact. It is how iOS Music applications interpret them. I have an iPhone 4S and iPAD2. Both have identical results, which is at least indicating it is a single problem preventing the Smart Playlists from working properly.
I hope this helps some at least limp along until a better/longer term solution comes along.