I don't think that you'll ban anyone...I could be wrong. However, Adsense might ban YOU if you iframe the code.
Even if they don't ban you, you might start getting public service ads, and those don't pay anything.
You will not be banned, imo, ad servers usually serve in iframes to make ad serving faster and less laggy for websites and if you pick Adsense as your backup network it will be served in an iframe. I have been using it for 2 years and as you see I have no problems, the only but is that the iframe should be without content, no attributes with stuffed keywords.