Hi Fred and welcome to the forums.
It sounds like you have everything configured so in theory it should work. I’ve never personally isolated VFD traffic from the primary controller that is controlling it. Is there a specific reason why you don’t have it on the same network? My concern, is with delay and the overhead of managing the routing to/from the drive.
Be sure to keep us posted on this as I’m interested in knowing how things work out.
the other Fred!