Yes, I believe it is justified to pay disadvantaged students to further their education. Giving disadvantaged students the opportunity to continue their education not only provides education to those who may not have had the opportunity available, but it would also help the economy by allowing people of different parts of life have the education for better paying jobs and become higher earners.
It is unethical to pay students, disadvantaged or not, to learn. Students should learn because they want to and, often, students who want to be students make the best learners. It is, however, okay to finance the educations of disadvantaged students who want to learn and who have demonstrated themselves as prospective leaders.