The official Blender exporter for Urho3D doesn't as yet support the normals modified by the normal edit modifier (although I was linked to a branch that looks likely to work, though I haven't as of this writing tried it out). To do the canopies, I simply exported to .OBJ and then used the AssetImporter tool to convert to Urho3D models.
That test tree is a tad on the heavyweight side. I'm still pretty poor at making trees. Still, the technique seems to work fairly well. It even works pretty well on my original test tree, to lighten it up a bit.
It could be a pretty useful technique for foliage. I really liked the looks of the trees from The Witness that SotL linked to, though I am looking for something a bit different.
Edit: Just tried the exporter branch, and it does work.