I created a shader tree to convert albedo/metallic/roughness outputs to Arnold standard shader inputs.
You can download the project here:
https://dl.dropboxusercontent.com/u/83350004/substance_to_arnold.zip

Test scene content:
a few mesh
substance (sbsar file from Substance Share)
lights

Arnold’s color management settings:
Display Driver gamma: 1
Lights: 1
Shaders: 1
Textures: 2.2

More info about that:
https://ddankhaziportfolio.wordpress.com/2016/05/01/maya-2016-arnold-color-management/

I used a ramp node to convert the metallic map into an IOR map. (Please use Fresnel everywhere. This is far more accurate than reflectance at normal workflow.)
lowest value: about 1.5
highest value: 13 (silver)

Don’t forget to update your Substance plug-in.
https://ddankhaziportfolio.wordpress.com/2016/02/12/substance-maya-plug-in-again/

Cheers, D