Engines like UE4/Unity are using real-time PBR shaders. Offline renderers like Arnold are using their own proprietary shaders. They are completely different shading models and are not compatible. Offline renderers are starting to adopt the map channels of real-time engines to recreate the material, but not the shader…
In particular here and here http://wiki.polycount.com/wiki/Modular_environments http://wiki.polycount.com/wiki/MultiTexture Best of luck! It's a fun topic to work on!