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I'm not sure if there is a spawn model command for hoi4. If you want your model in game you would have to make a mod that replaces one of the nations unit models.
 
I'm agree it's the most easy way to test units.
So I did that for the US rifle and I got those errors:

[14:12:15][pdxassetutil.cpp:309]: Failed to create material with shader PdxMeshHoI4
[14:12:15][pdxmeshtype.cpp:390]: Pdx mesh type with no meshes: gfx/models/units/USA_infantry_weapon_rifle.mesh won't render.

why?
 
Maybe you didn't add the "shader attribute" on the phong shade ?

-Select your phong shader object
-Open the pdxExport pluggin, section "Selection"
-Click on "add"shader" attr."
-Assign your phong shader object on the polygon object you need to export if it's not already done.
-Export :)
I did add the phong shader to the mesh by clicking the attr. shader button and i assigned the shader to my object.