To watch Vimeo video in HTML5 player, open a video webpage, clicking the “Switch to HTML5″ button under the video playing window. The player will respond and load instantly. And then the video will start to play, you don’t have to waste time and wait for the video buffering. I don't know much about this. Click here.
When I open up a vimeo video on the Safari app on both my iPhone and iPad, they both work fine no problems.Now I have created an iPhone app which has a UIWebView and loads a vimeo player video and that works fine too.