Commercial meshes sometimes have more than one material assigned to them. So the video below teaches you how to get those meshes to be useful by separating the material in order to use them with JMonkeyEngine.
Have fun creating!
I did a simple model once, pressed for time I thought I’d try to import it into the SDK even though it had multiple materials - and jME has one mesh<->one material.
I was pretty surprised when the blender importer automatically split the mesh into separate nodes according to material 
I guess what I’m saying is, try the SDK first, it might do just what you need. If not, you can always do the trick in the tutorial for better control of the process.
@jmaasing is correct. But I say we officially support using multiple materials on one object to keep up with the industry standards.
I’ll see if I can contribute this into JMonkey.