It does work that way. It'll first search for the object the map needs in the embedded set of items (so every server and every player will have those objects), then in the associated titlepack files (if the object exists there, every server and player will have them all too), then in the Userdata folder (unreliable).
So if the players have all required objects in the Userdata folder, the map will load anyway (although the geometry may differ from what's intended, since it just checks the filename!).