Why does he say this. In a worst-case scenario, the paper can be peeled back by hand and a solution such as DIF can be applied to remove the rest of the paper and any residual glue. In fact, there are a lot of posts on this Forum (if you search the ENTIRE page for 'wallpaper') that talk about how to remove wallpaper. Using a Paper Tiger and DIF are all I use.
A vaulted ceiling, as I know it, is a vaulted ceiling. Am I missing something?! Also, my personal taste says to paint. If you can do a 2-tone as in the attached picture, that will add some character instead of using wallpaper.