You need to understand that you can’t take direct action on someone else’s webpage - image the security implications of that (you could host a banking page and capture user input, etc)
Therefore the options available for scrolling an embedded webpage are limited to what you can do in your own parent page - i.e. you embed their page in an iframe with a really big height, and then use JavaScript to scroll your own page.
This is not a function which Xibo supports and will be very difficult to get right if your page gets longer and shorter (as RL said).
Your embed code wont do anything because the first time it refreshes it will be on a different page and your marquee will be gone.