I spent some time trying to get an iframe into an article, no luck. I read what I found in this forum, and some googling. HTML cleaning switched off everywhere for anyone, iframe plugin installed etc. One success: iframes are not already stripped when toggling editor. But after saving an article, it's gone.
Joomla 3.4.5, JCE 2.5.11
I tested some more:
Standard article: When toggling the editor, all attributes are removed. Saving the article, the iframe will not be stripped - so as long as I don't toggle, it's ok.
Text in JEvents: attributes removed on toggle, iframe stripped on save.