This week's book giveaway is in the General Computing forum. We're giving away four copies of Arduino in Action and have Martin Evans, Joshua Noble, and Jordan Hochenbaum on-line! See this thread for details.
Whatever is used for Hibernate/JPA caching is for DB contents only. Standalone caches can be used for all kinds of data, wherever they originate. In that sense it's not much different from EhCache in standalone mode (outside of JPA). I don't think EhCache can be used by non-Java clients, though.