Arriving at CDG, Paris @ 7:00AM on Christmas day. Will I be able to get a taxi that morning into the 1st Arrondissement??
Yes, you certainly will be able to get a taxi.
If you want to save money, take the RER B to central Paris and the Metro to the station closest to your hotel. They'll be running, too. The fare, including unlimited transfers until you exit the system, is €8.50. See the Paris by Train site for detailed instructions, including photos.