So, I have found that the only jbpm call that disregards the db connection that was set on the context using JbpmContext.setConnection is the call to createSchema.
If the connection is set on the context when createSchema is called a UserSuppliedConnectionProvider exception is thrown with the message "The user must supply a JDBC Connection"
This appears to be a bug in jbpm not passing the connection down to hibernate.
As a workaround, I found that setting the property hibernate.connection.url will force hibernate to find the database connection that was already established.
please file a jira issue for this and better yet, attach a proposed patch.