You cannot directly upload YouTube videos on SlideShare in LinkedIn. However, you can add YouTube videos to your SlideShare presentations. Please find the instructions below- http://help.slideshare.com/entries/102264-how-can-i-add-or-embed-a-youtube-video-to-my-slideshare-presentation#overview

Once this is done, sync your LinkedIn account with your SlideShare account and the presentation containing the embedded YouTube video will show up in your LinkedIn account as well. Check this link  to know how to sync your account.