local. A warning would be helpful.. to protect us, from ourselves. 
I have a very similar problem.
1. I used the local template to build a scene.
2. I added the two layers below to that scene. Those two layers are both in the same coordinate system. Besides the two layers I have added, there is the default Topographic layer. No other layers exist in the scene.
a. a bare earth DEM created from las files as a raster in a file geodatabase (called DEM below).
b. an index of the the las tiles (from which I built the DEM) as a polygon shapefile. (called TILES below).
I want to see my DEM in 3D, but I cannot add it to the 3D Layers group. However, in the 2D Layer group, it does draw, just flat.
I CAN add my TILES to the 3D Layers group. but I cannot pan the scene view in a 3D-way. The view only zooms in and out with my mouse wheel.
I have set my DEM as the Ground in the Map Properties>Scene>Elevation Surface properties
What I see is a very strange picture.
Can anyone help?
Thanks!
Sam
So I would try a couple things. First make sure to set your DEM as the ground elevation for your scene. Then try removing the Esri elevation surface. This will set your DEM as the ground surface elevation. That may help fix your problem.
Now I might be mistaken on this but I don't believe a raster can be a 3D layer. I think all 3D layers currently must be vector. However if you set your ground surface as your DEM then add it as a 2D layer, it should drape over the DEM Ground surface creating a 3D view. Similar to adding an aerial. 
