For our theater and cave I have made a very simple VRPN plugin that supports VRPN Tracker and Button devices.
You can download the source here: https://github.com/PjotrSvetachov/VRPNInput It needs to be placed in the UnrealEngine\Engine\Plugins directory and you need to build the engine from the Github source for now.
You will also need to have the VRPN library compiled with the same compiler you used to compile UE4 with.
I have managed to complie the VRPN library with both Visual Studio 2013 and with Epic’s Linux crosscompile toolchain. Precompiled VRPN libraries can be downloaded from from https://github.com/PjotrSvetachov/VRPNInput/releases
VRPN devices can be configured using .ini files and you need to provide that path to the file as a command line parameter for both the editor and engine. I admit that this is not ideal but this is something I started working with and in our situation it’s handy when you need to switch devices or remap buttons without repackaging the project.
As a example of this configuration file is provided here: https://github.com/PjotrSvetachov/VRPNInput/tree/master/VRPNInput/Config
The config file will provide a blueprint event like this one:
I hope that this will be useful for some people. Also any contributions are welcome.