Is it OK to let a one year old child sleep in his own separate room?

I don't see why not. Make sure they sleep in between you and your spouse or have a rail up on the sides of the bed so that they don't fall out. If you don't want your child to get used to it then I wouldn't do it on a daily basis. They won't want to sleep in their own bed and it will be doubly difficult to get them out of your bed when they get older.