you need to instruct kie server to use different (than default) data source and dialect. You do that via system properties:
-Dorg.kie.server.persistence.dialect=org.hibernate.dialect.PostgreSQLDialect -Dorg.kie.server.persistence.ds=java:jboss/datasources/psjbpmDS
change the JNDI name of the data soure that matches your environment and that should do the trick. Though this is for kie server only, for workbench you need to modify persistence.xml that resides in jbpm-console.war/WEB-INF/classes/META-INF same stuff needs to be changed