Generics are a part of
Java 5, not Tomcat. But since Java 5 is required to run Tomcat 5 (unless you go the extra mile and install the Java 1.4 compatibility package), you can generally use Java 5 code when running under Tomcat 5.
EL is part of
JSP, and supported out of the box. I think JSTL needs to be installed separately, but all that involves is dropping two jar files into the common/lib directory and you're done. Struts, too, is a separate install (although that would be part of each web app that uses it, not of Tomcat itself).