Using the SBSAR materials is actually pretty simple, but only one at a time, not an entire library from what I’ve seen so far.
In the ‘Materials’ dialogue where you can ‘+’ add a material, when you click the little triangle in the bottom right corner of that button, it lets you change the type of material you want to add. Change that to ‘Substance’ and it will open a dialogue box asking to choose a substance material to add.
I would still much prefer the ability to link a LIbrary folder to my Substance library so they are all available without having to add each one individually, or at least be able to see each one like we do with the Sketchfab parts and can see the material before it actually loads it into the project just like all the other materials and parts that can be seen in the library.