To use a Physical Sky for lighting, first, create a Skydome light (Tab > Arnold > Arnold Light. Change Light Type to Skydome). Change Color Type to Shader. This will add the Color Shader parameter showing the location of a vopnet that is contained inside the light node for convenience.
A Physical Sky shader can be added inside this vopnet and connected to the color parameter of the Light Output.
If the Physical Sky is also required to be visible to the camera, reflection or refraction rays then an Environment Output can be created in the same vopnet and the Physical Sky connected to the background input.
This shader can then be linked to Environment parameter of the Arnold ROP.
Alternatively, a vopnet could be created in the SHOP and a Fetch node used to grab the Physical Sky.
For convenience, a material has been created at shop level which contains both a Light Output and Environment Output.