Consultants using old version of Hibernate ORM for new application - should I be concerned?
There could be several reason they continue to use an older version. It may be they've run into issues with newer versions and know to stay away from them. It could also be that they know the version they're on and can be much more efficient working in it which translates in to dollars.

I see later versions lost support for sharding and had an overhaul to services management. These may be features they lost that they like to use.

I would ask them to explain their reasoning for using the older version and then decide on what to do. 

This question might get better answers on Stack Overflow since ORMs are used by software developers more than DBAs.