It's actually dealing with the syntax of "create index" command, i.e. where the columns are identified.

Without the change, org.hibernate.test.unionsubclass2.UnionSubclassTest will generate this sql:
     create index UEmployeeAddressIndex on UEmployee (address, zip) 

which generates this error on Teradata:
*** Failure 3706 Syntax error: Must specify index field(s) for CREATE INDEX

The changed code will cause this code to be generated for Teradata:

     create index UEmployeeAddressIndex(address, zip) on UEmployee;