While HQL supports entity type expressions (see user guide 15.32) the envers query API does not support them.
I suggest to introduce four new methods on AuditEntity: entityType(Class entityType), entityType(String entityName), entityType(String alias, Class entityType) and entityType(String alias, String entityName) which all return an AuditCriterion. The first two are needed because we might specify the desired type either by entity name or by class literal (A translations to the effective audited entity name must be made in the implementation). The other two methods are necessary such that a custom alias can be specified on which the type check should be applied.
This example will only return those entities of type EntityA which are really of (sub-)type EntityB.
I will try implementing this and will provide a pull request for master.