In this case, Yes, sleep in the airport. DFW has not one but two Hyatts (a Regency and a Grand) in airport terminals, with the Grand Hyatt in/above the international D terminal. The entrance to the hotel is inside the terminal and something like 100 feet from the security checkpoint. This means not having to pad your schedule to deal with the variability of a courtesy shuttle. And, with a layover less than 12 hours, you could through-check your bags so as to not have to deal with that in the morning. You could get more or less a full night's sleep with the layover you mentioned. I've done just this at DFW several times for international AA award tickets.