I hope this post won't be regarded as spam, but as something helpful for the community.
I have developed, along with two fellow students, an eclipse plugin able to generate hibernate mapping with a visual interface. It can import XMI files from Umbrello UML, reverse engineer MySQL databases and import DDL files.
It includes a lightweight UML and DB logical view editor too, and there is a standalone version available too (even if it's a little outdated).
This is an opensource project developed at Politecnico di Milano, so contributors are welcome.
The plugin can be found at
gnumler.sourceforge.net .