Hi Steph Anderson
Chrome's update will apply to all web pages, including your Marketo landing pages. If you have an SSL cert in your own website securing those pages, your visitors won't get that warning from Chrome. However, your Marketo pages aren't hosted on your website, so they wouldn't have the SSL security unless you have an SSL cert added in Marketo.
We have a doc relating to this change here: Upcoming Changes to the Chrome Browser
Hope that helps!