I have created a smoke sim at SOP level. When I use a Merge node to combine the Pyro Solver output with a geometry object I am using as a collision object they show in the viewport together, but when I render (Mantra) the smoke does not show. Is it not possible to combine them in the same render?

I am trying to also render the collider geometry brought in to the Geometry level with a Object Merge node.

Would I need to render the geometry I am using for the collision object by using a separate Geometry node at Objects level so it renders with the Geometry node that holds the pyro sim (both Display flags activated - blue)? Will this method create the proper occlusion between smoke and geometry, or is there another step like using a Forced Matte in Mantra to occlude the smoke with the object? Would I need to render each separately and combine them in Nuke?

Don't try to render them from the same Geometry OBJ. Create 2 Geometry OBJ nodes, use Object Merge to bring your pyro sim in the first Geometry object, then do the same with your polygonal geometry but for the second Geometry Object.

Will this method create the proper occlusion between smoke and geometry, or is there another step like using a Forced Matte in Mantra to occlude the smoke with the object? Would I need to render each separately and combine them in Nuke?

They will still render together and create the proper occlusion.

Thanks everyone, I will try it.