I don't know.
This page says "With very few exceptions, Servlet 2.3 web applications should work fine in a Servlet 2.4 container.".
The servlet spec says "For backwards compatibility of applications written to the 2.2 version of the API, Web containers are also required to support the 2.2 version of the deployment descriptor. For backwards compatibility of applications written to the 2.3 version of the API, Web containers are also required to support the 2.3 version of the deployment descriptor. The 2.2 and 2.3 versions are defined in the appendices."
If Tomcat is fully spec complient, it should be ok. But is it really ? JSP, I'm not sure. If you are trying to upgrade to a new container, you'd have to
test everything anyway.