1. No. You are right, JBoss Cache does not support that mode and Hibernate will not activate it.
2. Yes. Ehcache does not support clustering.
My suggestion? Replace nonstrict-read-write withtransactional in the mapping files and rebuild jBPM. A more advanced optimization is to replace with read for definition objects. In this case you might need to disable the second level cache at process deployment time, as the read cache strategy could prevent updates from arriving at the database.