Welcome to SPCR.
Allegorithmic says nope. But, I think they are just speaking to multi-gpu use in their s/w and not multi-gfx cards in the system and only one used for Substance Painter...
If you currently have a motherboard with integrated graphics, and you only want to use the other monitors to display non 3D information (browser windows, Netflix, etc), you could try connecting the secondary displays to the mobo's gfx outputs. See how that works. You
might be able to do this as well with two Nvidia cards...
this FAQ is useful..set up a profile for your programs and tell them which gpu to use..