Thanks, B2N2 for your analysis.
I think the pilot situation in the US is similar to many places around the world in that fewer instructors are moving up to the regionals/airlines and maybe the school has already foreseen an oversupply of instructors in its ranks for the next year or so.
That would leave my friend "out in the cold" with an M-visa, which does not achieve his aim of accumulating hours after his training.
On the other hand, another Florida school who is famous for promising so-called airline interviews for students is welcoming my friend with open arms under a J-visa. I have already warned him against confusing "prospects" with quality flight training. Besides, I believe he hasn't got any chance of employment without US residency.