Please remember you have only imported Gerbers into FAB 3000. Gerber files are just X,Y coordinates plus shapes -- it does not have any net information, or other intelligent data.
Netlist:If you want nets in your ODB++, you'll need to extract them from the Gerbers using Netlist extraction. Here's a tutorial showing how to, https://numericalinnovations.freshdesk.com/support/discussions/topics/14000003465
Symbols:Symbols in ODB++ are "custom apertures". You sample Gerber files only contain basic shapes like Circle, Rectangle, so there is no need to generate ODB++ Symbols.
Here's a quick tutorial movie (no sound) showing me correctly assign your layer types (chose Neg Plane instead of Internal with "Neg viewing"), and extract netlist. Now when I export an ODB++ it will have the nets. https://numericalsoftware-update.s3.amazonaws.com/tutorials/2018-08-02_7-54-11_gerber_odb.mp4
Tutorial Movie Notes: I understand this is just an evaluation design so there were several things that didn't make sense, so I just made assumptions.
1. I was confused by the layer types for the first minute in the movie.
2. Drills were imported with wrong scale so I scaled them by 10X. Although your gerbers already had drill information.
3. Obviously I would need to setup blind/buried drills correctly - but I just extracted the nets anyways. Here's info for Blind/Buried setup, https://numericalinnovations.freshdesk.com/support/discussions/topics/14000002569
Thanks again, and please let me know if you have any other questions.