I just installed the module on a local test site and reviewed the code, it doesn't look like it stores anything site specific. I also created a second test site and was able to confirm my suspicions, and use the single content block on both sites. So yes it will work...
... although I'd be careful of using this module on a large scale i.e.: managing the majority of your content. I believe it would work well in a small example where there is some static content only or a multi-site wide notification of availability or something like that but nothing like news, events, etc. Kentico is built off of using Document Types for content and this pretty much bypasses all of it, good idea although only for special needs.
I'd look for an rss feed or RESTful service or something like that you can utilize across both sites if you need larger scale.