I was wondering if it is possible to customize the interface of the Flex viewer with HTML using the index.html file that is located in the viewer?
The Flex Viewer is an embedded SWF file that is wrapped up within an HTML file.
By default the SWF is set to 100% width and height.
It is possible to add banners, logos, etc around the SWF content.
I could not find a FlexViewer example, but this is a Esri Flex app - click View Source on the blue html header/footer.
Personally, I prefer to directly modify the look and feel of the Flex app, and this has been a made a lot easier since the Flex 4 SDK with skinning.