The command bpy.ops.export_scene.mitsuba is the exact command run by blender when using the export option in the UI, so it is likely that this does not work either. Are you sure the add-on is properly ...

ERROR: initialize: Your system's graphic drivers seem not to support OpenGL 3.3 / OpenGL ES 3.0, sorry : ( Try a drivers update, buy a new GPU or try software rendering on Linux; Godot will now crash ...