You can, with the caveat that our platform is primarily photo-based, and so a photo is required to be uploaded with every entry.
How does that work? We have run photo contests where entrants provide a photo and could also provide a URL to a YouTube video. (Participants are required to upload their video to YouTube first, as we do not have a direct way to upload/collect videos). The YouTube ID is automatically pulled from their YouTube URL, and the video is embedded with the photo on an entrant’s voting page.
Here is an example of an entry in a previous contest that has a YouTube video included:
www.gogophotocontest.com/animalidol/entries/163102