Hmmm, that sounds right... The smoke from the fireplace is oxygen deprived, so it would choke the combustion inside the rocket stove.
BTW couple of years ago I sow a photos of project something similar to this one. Only that one was a fireplace which exhaust smoke was fed horizontally in adjacent rocket stove. Unfortunately I can't find it for the life of me.
And yes, it is too much of potential problems just for the viewing pleasure of the open fire.
I couldn't picture your idea on "
batch box with a high heat glass top". But these are the other ways I've come across, for viewing the fire insire the rocket stove:
http://youtu.be/g-Gjztwtokw?t=343
http://www.canadianoffthegrid.com/beauty-mass-rocket-heaters/
and
others.