If you take a look at the JPA specification, it specifically says that portable applications must list all the classes they include when running in Java SE.
The reason for this, is that because the JPA provider does not control the deployment environment, there is no guarantee there is even a way for the provider to discover the classes. It is possible that that information is simply no available to the provider.
TopLink Essentials is capable of attempting to find those classes. And when you change the default <exclude-unlisted-classes> value in Java SE to false, we will try to find those classes. Depending on your deployment environment, we may or may not be able to find them.
Where are your persistence units deployed (app server? which one? web container? which one? simple java se? Can you describe the packaging? (jar in an ear? simple jar?) If you tell me that, I can take an educated guess about whether we should be able to discover the classes or if you are just out of luck.
Having said that, I should reiterate that the specificaiton recommends listing your classes when running in SE.
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