display a vimeo frame in a view
As per this support request in Views issue queue: Views: Rewrite field, strips some HTML tags (SOLUTION/WORKAROUND FOUND FOR STYLE TAG) Views strips out certain tags. It does this using filter_xss_admin, which if you look at that API entry calls filter_xss, passing in an array of allowed tags. iframe is not one of those unfortunately.

So I think that you might need to do a workaround. I would look at two ways of doing this:


Rewrite the outut in a Views template. You click on Theme:Information at the bottom of the advanced pane in Views UI and you would select the theme file for the Vimeo field. More at An Intro to Drupal Views Templates and Theming
Create your own theme function to output the iframe. Enable Views PHP and call the theme function from a rewritten Views field.