Depending on the reason. If his parent(s) is/are ill, or have to live alone because their only child is getting hitched, I'd be pretty open to the idea. However, I'd prefer if they were to move in, they'd come after the newly wed stage, seeing as those years are the break it or make it period.
My grandma lived with us since I was a kid and I learned a lot from her
I'd love for my kids to have the same experience.