Is is possible to have Windows Server (the big one with UI) as host OS and Windows Server Nano as container OS?
My guess would be yes, but I haven't tried it with Nano myself.
What I do have running, however, is Windows Server with GUI, which in turn runs dozen Windows Server Core containers. Since you can select either Core or Nano as the container OS, I don't see why would you have any problem with Nano.
The reason I didn't try Nano is because it supports only 64-bit apps, which is, unfortunately, not something I have available right now.