persistence.xml is for JPA/EJB3 so not relevant for JDO. Yes, you could probably use Seam with JDO but I don't know of anyone doing it. Seam shouldn't need JPA or Hibernate to run, so report issues here. But you will loose a lot of the power of Seam as there is no integration.
I think to implement a web application which is independent of the persistence layer: If I want to change Hibernate by JPA, the changes must be minimal, that's why a thought about a delegator, which will manage the persistence layer. Sincerely I didn't find out how to do it yet. It would be nice, if changing to JDO would work so easely too.
What would I loose, If I use JDO instead of the other two?
If you know any link please let you.
Thank you in advance.