I think we need some more information here. What exactly do you mean "integrating the current forms" - does that mean you're using the existing forms, and reposting the data into Eloqua? Or are you re-implementing the forms within Eloqua?
In either case it's not clear to me why having the forms inside an iframe makes a difference. An iframe is sort of like another browser window embedded in the page. It simply shows the content of another URL. So the form inside the iframe is really another web page, so you have to integrate that page with Eloqua in some way, however you're integrating the forms that work.
What system is hosting the iframed forms? Is it the same as the rest of your website? Why are they in iframes? How is that interfering with integration?