The rsync setup is a bad idea in all honesty, outside the fact you will have multiple physical EE installations, and if you go by the book, multiple EE licenses, you also have multiple copies of EE you need to update. File uploads, EE caching, if you use page/template caching for instance, when you publish a new article the caches are flushed, but the only system that would have the caches flushed would be the system that executed the publish, the other system would be unaware. There are other complications to consider too, but rsync of files/content in a load-balanced environment works great with all static content, but poorly if at all as you expect it to when you are dealing with dynamic content, file uploads, caching, etc. It can be done, but its way more complex, and prone to complications then a central storage solution.
On that note, you would be much better off adding a NFS file server, and/or an iSCSI/Fiber Channel storage system w/a clustered file system, but NFS would be the easier to implement and manage. This gives you a single copy of EE, shared caching and other files, etc. EE is at that point working across multiple servers but to itself looks to be on a single server, as of course from a files standpoint is. If they are worried about single point of failure then suggested to use a redundant head-unit NFS system from places like Netapp, EMC, Nexenta, or others.
EE nor most other webapps will have a problem “sharing” a single mysql server as really mysql is working based on an authenticated connection, executes a query, returns data. Be that from localhost, a single web server IP, or 10 web server IP addresses, as long as you have privileges on the mysql database, its not an issue.
Finally on your diagram included though I am not sure the separation between ExpressionEngine and the IBM HTTP server above. Are you going to be using the IBM HTTP servers as a proxy in front of EE running on apache/nginx or similar? If not then really those would be combined as EE really is a web application rather than a stand-alone server appliance of some sort.
Just a few things to consider, but EngineHosting runs EE, and many other web applications in a load-balanced environment in a very similar fashion. The technology vendors are different, but load-balancers, web servers, central storage (NFS based) and separate MySQL systems all come into play. Have been doing that for many years, across many thousands of small and large sites alike. In the end, its transparent to the web application.