Hi Andreas,
Yes, the Unity SDK package is based on .NET/Mono and can be used for standalone .NET applications as well. We even include a WinForms example that you can use as inspiration when building your application.
We still do not have any WPF sample, but might add one in a separate .NET SDK package later on. Until then, you can take a look at the WPF application that @maroonedsia has been kind enough to share with the community: http://sdrv.ms/1bnVhyA