GEFanuc offers a product called Cimplicity HMI for CNC. It is an add-on to Cimplicity Plant Edition. Part number IC646NCN010. It communicates with the CNC controller via GE Fanuc's proprietatry HSSB (High Speed Serial Bus), so you need a HSSB interface card in your PC.
That's probably what the Fanuc rep is recommending.
The problem with writing your own interface with VB is that Fanuc does not publish the details of their serial protocol. There are a lot of Fanuc CNC controllers out there, so there may be some third party ActiveX or OPC controls avilable that you could integrate into your application. I've never investigated along those lines.
Using Cimplicity will mean higher up-front costs, but will assure you of a level of support so you can get your application running in a reasonable amount of time. If you try the VB route, there is a good chance that you'll burn up any initial cost savings in additional development hours.
You get to flip the coin and make the call.