Speaking as a parent of an emotionally healthy, well adjusted loving 25 year old son, I firmly believe that as long as the baby is left with someone who will care for the baby with love, and that would usually include the child's grandmother, a night on the town may be exactly what the parents need to be able to deal better with the stress of parenting a newborn. Babies are difficult to care for. Parents NEED a break to be the best they can be for thier babies!
do you have any kids?
I think it's alright, as long as they don't do it too often.