It would depend, for me, on how he handles the snake.

If he has a large cage, and the snake can stay in it all the time, then I honestly don't see what the problem is. You could have him keep the snake in the room he is staying in, and keep the door shut all the time. Then you would never have to see it. I would also specify, if it were me, that he feed the snake only when you are gone. That is the problem I have personally with big snakes ... I like them, but I don't want to see or hear one eating its dinner, if it eats live food. I know its natural, but it bothers me. I wouldn't want to be home when that went on. But if you never see it, hear it, and you know it's going to be in a secure cage all the time, I would do it, as a favor for my family member.

If, however, you think he will not abide by your wishes and will let the snake out of it's cage if you don't want him to, then I would say no. It would depend entirely on how responsible, courteous and respectful you think he will.