I am just about to try to print double sided using a single sided printer and an OmniGraffle document. The method appears to be to print the even pages using the printer driver, then reverse the printed pages and return them to the printer feed tray with the document top facing downwards. The issue I am trying to solve is to have the front and rear printed sides in registration and I wonder if OmniGraffle can do this automatically. I have searched for page spread but have drawn a blank.
I don’t think so, not as a ‘native’ feature.
You might be able to create a PDF of your document and use Preview to handle the layout.