Foreign-born Asians and Hispanics“have higher rates of intermarrige than do U.S.-born whites and blacks.”

是倒装语序。主要因为than从句的主语较长，为了照顾匀称而倒装。可以还原为：

Foreign-born Asians and Hispanics“have higher rates of intermarrige than U.S.-born whites and blacks do.”

Foreign-born Asians and Hispanics“have higher rates of intermarrige than U.S.-born whites and blacks have.”

主句的宾语因为含有比较项 high，than 从句不能重复出现。即：higher rates of intermarrige，high rates of intermarrige，以及被higher 修饰的 rates of intermarrige，都不能出现。