Randomly, my PU bundle doesn't start its services because it keeps waiting on the Hibernate OSGi services availability.

This has been discussed with Brett Meyer, who has also identified this in the official Hibernate OSGi example code (https://github.com/hibernate/hibernate-orm/blob/master/documentation/src/main/docbook/quickstart/tutorials/osgi/managed-jpa/features.xml#L65).
Brett has managed to workaround this issue by forcing the start-level of some bundles, but this is not possible in Fabric8, and is not fully compliant with what OSGi proposes as modular design.

I'm providing example code that you can easily get up and running and see for yourselves. All you need is Java 7, Maven 3.1.x and to download fabric8-karaf-1.0.0.redhat-340. Instructions are available and have been tested!