Do gif links that end with .gifv not work with the tags?[/QUOTE]
No they won't work because gifv is just a URL extension on imgur (and not a real file format); they convert very large .gif files into WebM or MP4 video. The result is they are smaller and faster but also means you can't share them as images, because they're not images.
Do gif links that end with .gifv not work with the tags?[/QUOTE]
Try the same link but manually remove the 'v' on the end, so it becomes just a gif extension. Works with IMGUR unless the original file wasn't a gif to begin with.
[IMG]http://i.imgur.com/AoUN3oG.gif