I think this is a very complicated question that might not possibly be answered on a messege board.
All NCAA students are allowed 5 years of eligibility and 4 years to compete. Those that have taken a redshirt and can complete their bachelor's degree in 4 years are allowed to take credits as a grad student and still play fifth year.
Since there are many qualifications for entering grad school, you might be best served by going to an academic advisor with questions. I also am not sure if there are any rules regarding this governed by the NCAA. So you might want to give them a call as well.
The only stumbling block may be that there are, I would assume, very few coaches that will take on a 5th year first time player.
It may be best to consider an early transfer to a school where there is a graduate program, however very often credits are lost in the transfer process. The good part is that he would be able to use all of his eligibility remaining.
These are complicated questions, I would seek the advice of an experienced school advisor.