Seems like the most ethical thing is for the student using such a GTP to enroll in a community college and for the GTP college to accept that and give transfer credit (including subject credit) for the community college courses, since community colleges expect many students to transfer to four year colleges. A student with financial limits may find the doing the first year at a community college is a way to reduce cost as well.
Of course, this depends on having quality community colleges available, which seems to be more true in some states than others. It also may not be suitable for premeds due to medical schools looking down on community college courses.