In their new addon they are supporting export of Principled BSDF node.
Blender glTF I/O no longer requires the use of custom Cycles nodes when exporting PBR materials. Properties of the Principled BSDF node will be used automatically, as supported by the glTF 2.0 format. Only simple node inputs like Image Textures are currently supported, and complex node graphs are ignored.
I just tested it on gltf model imported from sketchfab, exported with this addon, and loaded fine on jme.