Great news,
The latest Substance plug-in (1.4.0.0) is debuted in Maya 2019 and it works really well.
(Soon this will be released for the older Maya versions as well.)

I put together a simple example to see how can you use it.
(Mixing two Substance material based on their height map differences):

• The two main aiStandardSurface shader are mixed via a aiMixShader.
• For the mask I used a floatLogic node combined with a floatCondition node.
  The base was the two height map – generated in exr format :).
• For the dispalcement I used the bult-in aiLayerFloat node to get correct results.
• The whole shader tree:

The rendered image:

Best place to get Substance materials/files is the Substance Source site of course.

If you’re never used the pug-in before I recommend you to go to the official Substance channel (Substance in Maya playlist).

Cheers, D