Not sure exactly (too lazy to look at the code too), but you might have luck listing the Tomcat services before the EJB container services in jboss.jcml.
Might work... for the definitive look at the org.jboss.util.ServiceControl
Or wait for 3.0 to go final and use the dependency system to enforce order on shutdown.
Well, from looking at the jboss.jcml and the corresponding code, it looks like tomcat should be shutting down before the ejb container; however my experiences would seem to indicate otherwise. Is there something else going on which might make the EJB's unavailable during the tomcat shutdown?