1) Yes. The only extra configuration step is to include the necessary JAR files from the jboss_home/client directory in the WEB-INF/lib directory of your WAR file.
2) You need to make sure that your JNDI properties in your WAR file references the correct location of JBoss AS. If Tomcat and JBoss AS are on the same machine, you can leave the JNDI properties at their usual default settings. If JBoss AS is on a different system, you need to use the currect hostname or IP address in the properties.