1- it might be an overhead, but is not if you do it right. of course assembly code could be faster, but it all depends on the developers capability and how many resources you have. Hibernate makes your life much easier, so that the team will have much more time to focus on other things than mapping and SQL, for example performance tuning, so in a limited time (real world!) you could end up in a better performing application.
3- JPA is a specification based and insipired on Hibernate, so to say "using JPA" is an abstraction of "using Hibernate, or toplink, or openJPA, or.." but in most common cases it just means "use Hibernate".
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Rad 7 comes with JPA support and there fore they need to use JPA
I don't think they need to use it just because they got it; having paid for it doesn't mean that it's better.