Hello,
i have the exact same problem (an application that uses struts 1.2 and works find out of the box with other containers). Did you find a solution?? :(
Caused by: java.lang.ClassNotFoundException: org.apache.struts.taglib.MessageTag from [Module "deployment.xwiki.war:main" from Service Module Loader]
at org.jboss.modules.ModuleClassLoader.findClass(ModuleClassLoader.java:190)
at org.jboss.modules.ConcurrentClassLoader.performLoadClassUnchecked(ConcurrentClassLoader.java:468)
at org.jboss.modules.ConcurrentClassLoader.performLoadClassChecked(ConcurrentClassLoader.java:456)
at org.jboss.modules.ConcurrentClassLoader.performLoadClass(ConcurrentClassLoader.java:398)
at org.jboss.modules.ConcurrentClassLoader.loadClass(ConcurrentClassLoader.java:120)
at org.jboss.as.jaxrs.deployment.JaxrsComponentDeployer.deploy(JaxrsComponentDeployer.java:63)
... 6 more