welcome to the forum.
That depends on the application. You might consider that each remote access will have extra costs (latency, network traffic).
The best approach is to keep the application wich are communicating a lot togehter.
i.e. if the JBoss web-app call several EJB's for each request and apache keep the static pages and route the dynamic to the jboss-web which call EJB's I would keep the EJB's together in the same web-app instance and call the EJB local.
BTW, are you talking about JBoss AS5? In that case you might be in the wrong forum, nevertheless the questions does not depend on a specific AS version.