Is it unethical for employers to select applicants on the basis of measures even if the scales that such items measure have been shown to predict job performance?
No, this is not in any way unethical. So long as the measures actually are related to the performance of the job for which an applicant is applying, employers can legally and ethically use such measures.
It would be unethical and illegal to use measures that are not directly related to job performance. For example, if a firm were to hire accountants only if they were above a certain height and weight, it would be illegal and unethical. Such a measure could be used to exclude women on an allegedly objective basis. It would be unethical because there is no connection between one’s size and one’s ability to be an accountant.
So, all measures are legal and ethical so long as they measure things that are truly related to job performance. Otherwise, the use of measures can be evidence of discrimination.