We use Oracle, PostgreSQL and SQL Server in our environment.

It would appear from the documentation that I cannot specify multiple drivers in the various configuration xml files. Only the driver from the configuration file used in the Configuration().configure call gets used. And I don't see a way to specify multiple configuration files.

Correct me if I'm wrong!

you can have multiple configurations; in each one you configure the connection options to one database / persistence unit / context.
Of course it doesn't make sense to have more than one driver for one connection.
To answer about advanced use cases like transactions across multiple different datasources you will need to describe much more your environment; Usually you will not define the driver in hibernate's configuration but refer to application server defined datasources.
Please post more questions about Hibernate or JPA in the correct forum
at
http://forum.hibernate.org/viewforum.php?f=1

It may be that I'm confused, but I think this is a Shards issue, which is why I posted it here. With Hibernate you're only going to have a single hibernate.cfg.xml file.

I'm using Shards and I have a hibernate0.cfg.xml and a hibernate1.cfg.xml. The driver_class is different for each (MS SQL Server and PostgreSQL). I've found that it will only use whichever I load first - not both.

Thanks,
Kevin