EJB Modules, Utility JARS, resource adapter files and shared libraries associated with an application are alwasy grouped together into the same class loader. THis class loader is called as Application class loader. By default each .ear file gets its own class loader but if you want to use same class loader for all the enterprise applications in your server then you do that by setting valuse of classloader policy to Multiple on the server detail page
Each Web Module i.e. .war file receives their own class loader, a WAR classloader to load the contents of WEB-INF/classes and WEB-INF/lib directories. You can modify this so that single classloader i.e. class loader of the enterprise application is used for loading all the web modules in that enterprise application. You can change that on WAS Admin Console by selecting the Enterprise application that you want to change and clicking on its class loader link.
The application class loader is the parent of Web Module class loader. So web module can access EJB or utility classes but EJB cannot access your servlet