The answer is yes. But there are some requirements need to be clarified:
First, if you are not the owner of video and that video has not been published by its owner yet, then you can publish and add tags for it.
Second, if the owner of the video has already published it, you won't be able to do so anymore. However, you can still contribute to the video by adding more tags, as long as your tags have not yet been added by the owner. Please notice that the owner of video is the person who created it.