I am having the same problem, last I checked it didnt work on BLOPSII either. I un-linked, and re-linked my youtube account. It says it renders for me on MW3, but never shows up on youtube. I called support, because there seems to be no other option for this type of topic, and the wait is 30mins + (still on hold, if i get anywhere I will post it). I have not been able to render to youtube sucessfully since the release of BlopsII on MW3.
Rendering works for BLOPS2, but does not for MW3. If you notice when you link your youtube (or under account settings) it says black ops 2 and nothing about mw3. This is since they switched the elite site over for blops2. I called support, they said that it should work. I have two accounts, and two youtubes and neither will upload. Guy at support said it must be a problem with my account personally, and that if I should unlink and relink if that dont work i need to call back with my case number so my account can be investigated.
I really think they had no intention of helping me. So untill i want to call back and wait on hold for an hour (if i dont get disconnected!), and then wait for them to investigate my account, there is nothing I can do. I expect that will result in them telling me I need a whole new account, or something rediculous like that because thats exactly how they run things. Pass **** off, and tell you everything works when it dont.
I think theres a lot of people who arent exactly happy with BLOPS2 and should be able to do things normally on MW3 no problem. A lot of my clan members bought it and switched back to mw3. This is not acceptable not by even lowest of standards.
If you have your Elite account linked with your YouTube account but the videos that you render do not show up on YouTube, then use this workaround: