If you're trying to load (insecure) embedded assets from your Marketo LP asset library on a secure page, you'll have mixed content warnings or errors (depending on the browser).
You'll have to provide a URL to look at this issue further.
We utilize Cloudflare and wanted to know that if there are any repercussions to throwing our Marketo domain behind it. Tracking, etc.
If you merely want to proxy your Marketo assets (i.e. PDFs, images, CSS, etc.) via a CDN, the primary Landing Page Domain doesn't have to be pointed to the CDN. You can instead add a new Domain Alias to your Marketo instance, and have that domain routed via CDN. This way you're guaranteed to not disrupt direct views of Marketo-hosted LPs (via the primary LP domain).