Ok, here is very rough source code for primitive support of the Space Navigator. Buttons don’t do anything, and range of the axes is assumed to be between -2048 to 2047 before being normalized, because that is what mine tracks to when I run the example program from the 3DxWare SDK. To compile you need the 3DxWare SDK, where the Inc and Lib directories must be placed in the ThirdParty directory of the Engine source code (for example, on my system it is in K:\UT4SrcCleanMaster\Engine\Source\ThirdParty\3DxWare).
I could not successfully make a binary plugin yet - I tried compiling it with Unreal Engine 4.10.1 source code, but I kept getting DLL errors when I use the official release - likely related to not uising Visual Studio 2015 to compile it - I only have Visual Studio 2013 at the moment. Maybe you guys will have better luck! Also, I am 99% sure that Shutdown/unloading of the module is not done correctly - I wouldn’t use this in shipping code until this is fixed. 
Oh - don’t forget to create the directory in your plugins folder - the repository isn’t quite set up properly - I’m new to Git, coming from Mercurial, so it’s still pretty foreign to me setting it up.
https://.com//
By the way, this should work in games too, just for the heck of it!
You can do what you want with the source, no strings attached. You just need to apply for the free 3DxWare SDK from the 3DConnexion website!
Good luck!