Worked for me with non realtime. (shrug)
As written already: In General it does work
Non-Realtime export in Cubase is a “Record process” so if you have a monitoring setup that switches to input monitoring on standard recording, it will switch to input monitor on non realtime export also. With input monitor enabled, you will not hear or export audio of the track in question.
If it works for you then as I said you use a combination of Input monitoring that disables Input monitoring on record automatically, or it is something else that you are doing different.
Opposed to that, realtime export seems to be a “playback process” and switches off input monitoring.
That said I must admit the last Version I tested this with was Cubase 8.0.40. So mayby they changed that in the meantime.
I do exports with vst plugins/instruments and external synths all the time in 9.5! And yes, It is a real time process. But for me it works every time.
OK, thanks again for all the thoughtful replies! It was the input monitor being on. 
Works great now without having to do real-time mixdown. That doesn’t make much sense to me though. What is the reason for this? Is it in the manual or just an anomaly?
That may explain why it works both ways for me. I have my auto monitoring preference set on manual if that makes a difference.
Add it to my drawer of Cubase mysteries … 
~A LOT~ of things may not make sense to some people because they come from something older.
Over the years… Steiny, and all of these companies, have had to make decisions that would seem intuitive to someone who grew up on a Portastudio… but not someone who grew up on Mp3s… and Vice Versa.
And THEN- things had to stay the same in version N because thats how they were in version N-1! So decisions that made sense in SX for someone with a MIDI rig from the 80s carry forward to V9 where everything is VST. It’s confusing.
But … never forget: they are German. One thing you can count on- there was a reason. For every decision.
We might not understand it. THEY might not remember why. But it wasn’t random. It made some sort of logical sense once 
Well put.