Tough question. If the maple syrup is bad for them you could kill them. Maybe feed 1/2 the chicks sugar and the other 1/2 syrup?
Are you talking about %100 natural maple syrup or the colored flavored stuff they sell in the store? If it's the natural stuff I might give it a try but if you mean the store junk I would stick with the sugar.
Table sugar is sucrose sugar. Fruits have fructose sugar. Milk has lactose sugar. Glucose and dextrose are also simple monosaccharide sugars.
So what I'm going to suggest is that they are ALL monosaccharide sugars that are immediately available to the body to be used as quick energy and so therefore very similar. I would (as a smallish scale maple syrup producer) be very comfortable giving my chicks a healthy, natural, product that I know exactly how it's been made, to my chickies.
You're right too when you say it has better nutrients. It has minerals, vitamins, amino acids, and I'm sure I am forgetting something else but HORRAY for maple syrup!