Hi Avi,
I have also used youtube videos on sites without using the scheme.org video markup and they have been showing up in serps as well. There's an interesting article, where this was tested by an SEO who also concluded that you don't need the scheme.org markup for Youtube videos:
http://www.reelseo.com/embedded-youtube-indexed-google/
Considering Google owns Youtube, I guess it's no surprise!
Adam.