I believe the only way to use Visio diagrams in glass tables is to
a) From Visio, export the diagram as an image (PNG, JPG, etc...)
b) In the glass table you wish to use that diagram, click the "Add background" button, browse to that image and add it.
c) If that's not quite what you want, you can use that as a pattern to "draw" new figures on top of it to replicate it.
I could be wrong, but a quick look at my ES indicates it is still like this.
