You have the idea - look up using weight paint to determine where particles spawn - I don’t have an example but have watched a couple videos on the subject. What I am suggesting is that you make the real in Blender before going into Armory. That way the particle system is not doing anything real time. Armory is just rendering objects. Lots of objects but only objects and not doing any physics or logic to create the grass
Check out this links https://blendersushi.blogspot.com/2012/02/vfx-paint-weight-and-particle-instances.html