Hi,
what is the use of positioning the servers outside the DMZ. If your firewall blocks everything but the alfresco address, a direct attack is only possible on alfresco server. To attack the filesystem or the database, you have to
a) hack your firewall - game over
b) or hack the alfresco server.
In either case, once the bad guys are on the alfresco server, they have access to the database and filesystem anyway, even using "alfresco system rights", which would theoratically allow to hack the alfresco server and use the information stored in the DB like audit traces, version control, userrights settings …
The only reason would be that inside applications are using the fileserver & DBMS server as well and you do not want to expose other data. If you have a HUGE DBMS server, thats fine, but Alfresco can deal with that. But regarding a file server, I would think about splitting them up anyways for both operational security and maintenance issues.
Norgan