Hello,

Generally that is not possible with our Search Web Parts because in the iframe is usualy displayed dynamically a content of another page - so it is obvious that the content of the iframe does not belong to the actual page and therefore it cannot be displayed in the search results, iframe loads content of another page.

But you can try to create a custom solution: Use a document crawler which indexes pages and then perform your custom search function which will pass data to the iFrame... take a look at the example... search through the content of an index and retrieves the results in a dataset from our Developers Guide:
Performing indexing and search actions

Best regards,
Martin Danko