I got stuck at this basic matter. I can't find any other way to obtain input but through CoreWindow class (handling KeyDown/KeyUp/PointerMoved events or calling GetKeyState in the loop). I thought that I had to deal with input device directly, but it turns out that interactions with generic HID devices are blocked for UWP applications. There is also a "low latency" sample among UWP samples, that uses some twisted method through creating dedicated XAML control, but it seems more like a method to coexist with XAML rendering loop while I'm dealing with non-xaml application.
Maybe someone knows a good workaround for this?