The author says that Hibernate's connection & transaction management are lacking but does not elaborate. I tried google but could not find anything substantial. Latest Hibernate specs also mention delegating connection mgmt in production environ to the application server, but do not elaborate.
Hibernate (on its own) doesn't do much in the way of connection and transaction management; at least not much more than you could do with JDBC. I would assume the rational for not doing more is because Hibernate is just an ORM layer, its not trying to replace other technologies that do much more for connection and transaction management. If you need more elaborate transaction and connection management you would use Hibernate with an application server or Spring. The Hibernate documentation explains how you can use a DataSource and elist in a user or container-managed transaction.