You CAN add smart content to any NON-HubSpot hosted website page using an iframe:
1) Create a simple template in your design manager, removing both header and footer and placing a richtext block within the content area.
2) Publish a website page or landing page using this template and your SMART content rules.
3) Use the URL of this page in an iFrame (goolge free iframe generator and you will have several options)
4) Emed <iframe> on your non-hubspot hosted page.
View an example here (4th section): http://demo.larmahil.com/