Yes, in fact with any Java EE 5 container, we should make it a policy in the examples to assume that the container is taking care of the persistence unit rather than Seam. Seam should only step in when the container isn't willing or able (such as with JBoss AS 4.2).
What? This isn't something that is mandated by the EE5 spec so how does this work? Looking up the EMF over JNDI only works in JBoss. The problem here isn't about EMF lookup, it's about whether the container deploys the PU or not (JBoss 4.2 doesn't for a war, whilst JBoss 5 does).
That's not true. If defined as persistence-unit-ref in web.xml (I know, silly requirement) a Java EE container will load the persistence unit and make it available in JNDI for that application.
5.3.1 of JPA spec:
"Within a Java EE environment, an entity manager factory may be injected using the Persistence-Unit annotation or obtained through JNDI lookup."
JBoss 4 did not support this. Hibernate on JBoss AS just happens to support putting it in JNDI
defined in a vendor properties (w/o the resource reference).