Unity uses prefab files (prefabricated files) which are game objects that can be templated in the project with defined properties. This is especially useful when you want to position your objects in your scene directly per drag & drop (visually) without using any code.
My question is if something like this is possible in iOS and Xcode 6, since for now I only found out that you can drag and drop images into the scene.
If you mean drag'n'drop 3d objects in Xcode the answer is no. Xcode provides wysiwyg methods to work with the UI and even data models but this does not extend to three dimensional constructs; it is a coding tool, not a level editor! To build 3D applications using Xcode and related SDKs the usual approach is loading scene data created using 3rd party software such as Blender, then programmatically traverse the graph to associate behaviors. There is support for doing this at SDK level. Look at the Apple examples to find out more, as your knowledge will not immediately transpose from Unity to Xcode: the building blocks are essentially the same, but the approach to putting them together is not.