CANbus to USB adapter, is optical isolation worthwhile?
Is this optical isolation necessary?


If you work in the office, probably not. Industrial environment is somehow different, motors are mounted on a production line over long distance. Current leaks are everywhere. If you connect a computer on a nearby socket, the difference in earth potential is such that creates ground loops.


  Am I really putting my computer at risk by not optically isolating it
  from the CAN bus?


Sure. Any industrial bus, like RS485, RS232,... I do have only isolated converters, even for my hobby. I don't have any confidence in direct connection, I guess it's just my habit after decades of industrial computing.

You have to see also what software you get with the converter. For many years a reference point was PEAK-System PCAN. You can have also some cheap isolated converters (under 100$) for programming the motors, but it doesn't say CAN, it can work only for dedicated drive (I know it is isolated CAN, because I made a teardown of it) 


  I need to programmatically command the driver board from my laptop
  computer using CANopen


You would also need an API that can send telegrams from your C++ app to the CAN bus. Preferably it needs to run in a real-time kernel, but this is very difficult using USB converter. Don't expect that if you buy a converter it will be plug and play. If you don't intend to write the CANopen Master, then you would need to buy the license. Therefore I would recommend you to first get the price for the software and only then buy the compatible HW device.