Hope This Helps!
I myself have not yet had to make the decision of if I want to stay in music or continue onto a different career, but if music is something that makes him happy I believe he should stay with his dreams.
Yet I do think It would be helpful to study something else as a backup, perhaps not something major that comes with too much work, but something that he enjoys and won't task him greatly. It would be a good fall back if being a drummer falls through and when he has free time it would be something for him to do.
To be brutally honest, its a bit hard to become famous or make a lot of money right away by playing an instrument and being a drummer might not always be the smartest choice, a backup job would also make sure he is making the money he needs to have the necessities needed in life. If he were to make a living as a musician that extra job wouldn't be needed yet would still be there to help.
So to wrap it up, I do not think it will interfere with his musical aspirations at least not in a over the top way, it could even be good for him although he doesn't need it at the time.