So, my question: is one letter from a professor and the others from industrial supervisors with Ph.D.'s enough?
Yes, absolutely.
Or should he look into taking a couple of classes to get additional letters from academicians?
That would actually look somewhat peculiar if it excluded reccomendations from people that he worked with. I would only do this if he expects weak reccomendations from industrial colleagues.
If he is doing chemistry research in his current job and has good reccomendations, his chances of getting into a good program are excellent.
Personally, I think he should just get an MBA and go for the cash, but that's beside the point. Anyway, any thoughts?
There is a glut of PhD / MBA combinations in the sciences, because many people have had this idea 10 years ago. It was true then (6-10 years ago) that you could jump into a high-paying job with a good MBA tacked onto a science degree. However, those days are OVER.