This little trick won't affect your in-game model, but it will be very useful for previewing the final rendering of your textures.
By simply changing Zmodeler 3's reflection texture, your vehicle will have reflections similar to those visible in-game, so it's possible to get an idea of how your vehicle will look without launching the game every time!
The env.dds texture won't impact your model in any way, since it's only found on Zmodeler. In game, the env.dds is simply the map reflected on your vehicle.