I'm making a website that allows other people to upload videos. I'm trying to host all these videos on YouTube instead of my own server so I use YouTube API to allow them to upload these videos through my website straight to my YouTube account. Is this illegal or against their TOS?
Read their TOS, it should answer your question then. I'm not sure your going to find a person who works at Youtube around here very easily...
Yes that is completely OK. They are in essence still uploading to You Tube and are still bound by all the rules and TOS just as you are. You Tube also as a partnership program that allows you to make money from your original videos here. You can also create your own group to discuss and upload videos you have in common with group members. I remember reading a while ago about groups with several members, like church groups, uploading videos to the same group account but I can't find the link for you, you will have to search it out, but it's there. There is also a script that allows users to upload to You Tube from your site.