The result of a placed OAM would be the same as linking to the HTML file using the Web Content Overlay (if in5 supported the OAM--it would just unzip the OAM and link to the HTML file). The files, and the method of embedding, are the same either way.
If the content does not scale, it probably has to do what the Edge code supports or doesn't support (inside of an iframe container). You'll see an image scale because in5 does support the scaling. If you want to send us a file, we'd be happy to take a look.