Jim Richards, thanks for your example - however I'm not able to get it to work and keep getting that new CacheException( "On-the-fly creation of JCache Cache objects is not supported...").

Hibernate creates one cacheRegion for each and every entity class and OneToMany relationship property.
Do I have to statically configure (and maintain) a <cache> for each region?

It seemes that the only reference to the default cache template is held by the ConfigurationMerger which is consulted in org.ehcache.jsr107.Eh107CacheManager.createCache(String, C) only.
But there is no actual reference to org.ehcache.jsr107.Eh107CacheManager.createCache(String, C) nor javax.cache.CacheManager.createCache(String, C) and thus the configured templaed is never used.

I'm testing this with Hibernate 5.3.0.Final and EHCache 3.5.2.

hibernate.cache.region.factory_class = cache
hibernate.javax.cache.uri = classpath:ehcache.xml