I think it all depends on the context. I've included some YouTube videos in my posts, but they have been relevant. For example when I write about animal behavior, it is nice to find a video that shows it off, and I think both my readers and everyone else is okay with that. The owners of videos on Youtube are able to turn of the ability to let their videos to be played on external websites, so if they don't do this, then I think they are okay with it.

I do however not think it is OK to just copy-paste a video into a post without any text and get reward from it. However, that is up to the community to decide by their voting behavior ;)