Use jMonkeyEngine with an external main loop

I would like to animated a 3D figure from a gltf model with jME. The 3D figure should be moving along a track on a 2.5D map, like in this video by replacing the moving triangle with a 3d figure.

This 2.5D map is based on GitHub - mapsforge/vtm: OpenGL vector map library - running on Android, iOS, Desktop and browser. which is running the Lwjgl 2 main loop libgdx/ at 9f72b0037cc98da57e783f177d7a993501308680 · libgdx/libgdx · GitHub

This would be the pseudo code for the 2.5D map Lwjgl main loop to render also the 3D jME animation:

while (running) { 

   switch OpenGL context to jME
   render animation frame into a 2D texture // performed in jME
   switch OpenGL context to main loop

   render map frame and blend in the animation from the 2D texture

Does anybody has experience with such an app layout and could provide an example?

Why do I not use the libgdx framework to implement the animation?
A 3D framework animation is very new for me and it looks easier for me to implement it with jME.

The relevant parts of my response on the github issue just to start the conversation going:
It would be 1000x easier just to do everything in JME or everything in libgdx. I predict nothing but difficulties on this path and the amount of time it will take you to get it working could easily have been spent porting the “other half” to the one engine.

well, you can just render view into texture, but like Paul mentioned, its just easier to do everything just in engine.