I’m only making use of Vimeo’s freely available APIs with this.
Anyone is allowed to make a video on Vimeo, and anyone is allowed to distribute that video (i.e. link to it) however they’d like.
You also have the ability to password protect a video, and distribute that password however you please as far as I know. I can’t see how this would violate any of their Terms of Service, but I also haven’t read them to be perfectly honest.