I have a database that I can see with rtWizard, but when I open it with MGED, nothing shows at all. As far as I can tell, the database loads ok, but no matter how much I zoom in or out, I can't see anything in the output.
MGED doesn't display geometry by default, it just opens the database. You have to tell it what to draw. The "tops" command will list your top-level geometry and the "draw" command will display it. Alternatively, you can open the Geometry Browser from the Tools menu to graphically see your geometry similar to what you see in rtwizard.