Vimeo embedded videos do not appear in Safari although they appear in all other browsers on the same machine. Not only do the video not play but the placeholder where the video should be on the page is blank. This seems to be Safari 5 related.
First thing that comes to mind for me is if you happen to have any Extensions installed in Safari. You might consider turning them off and reseting Safari from the Safari drop down in the menubar. Clear out caches and and website data.
If you are familiar with looking at the page source code and know how to enable and understand Safari 5 developer mode and debug features, you will probably be able to get a good amount of information for that. Keep me attuned and all the best!