No, there isn't a difference. A blackout where everyone sees a page with a particular message instead of the article they wanted is exactly the same as unscheduled downtime where everyone sees a page with a particular message instead of the article they wanted. If search engines and caches can survive one of them, they can survive both, since they are identical from an external perspective.
I'm sorry. but this is silly. I have a hard time believing that you aren't simply trolling here.
- Ryan