Yes, but only with a view to encouraging them to apply: thereafter it is a question of the best person for the job. It would be just as illegal to take on someone because they came from an ethnic minority, as it would be to take them on because they were white.
An advertisement to people of a particular race may, however, be lawfully placed if discrimination would be lawful in the circumstances - for instance, because being of a particular race was a genuine occupational qualification for the job. So, for example, a restaurateur may lawfully advertise for Chinese waiters for his Chinese restaurant.
