Hi everyone!
Can anyone explain what im doing wrong? My imported (or appended, nwm) models cant be operated through scene.meshes[i] or any other way. What is wrong? Example: Babylon.js Playground
Hey there, welcome to the forum! 
The model is loaded with a rotationQuaternion, which causes the rotation vector to be ignored. But once the rotationQuaternion is set to null then the rotation vector can be animated like below.
Careful with this. Nulling out the rotationQuaternion will also remove the original rotation that was set on the loaded model. Perhaps using addRotation would be a more generic solution.
Also another option is to call toEulerAngles on the rotationQuaternion before nulling it, if you just want to use the rotation vector.