Yes, I think if you need some help with the children and can afford to pay a nanny, there is nothing wrong with that. If gives someone a job and can be a help to you.
You should set reasonable rules and conditions. You have to be consistent and if you want the nanny to live in she/he must have reasonable hours of work and leisure time. Not be there to be the parent if you decide you want to go somewhere.
I know someone who become a nanny and after the employers knew she was reliable and the children got on well with her, they wouldn't always come home till very late at night. They thought it was ok to take advantage. After a while the children felt neglected because their parents weren't there when they wanted them and so their behaviour suffered.
It can be good for children to have someone from outside the family to care for them. In your own home they also feel more secure. Just approach it in a professional way with respect on both sides, including the children and there is no reason why it should not work.