Just asked a CM on the Disney Dining line and she said that your dining voucher WILL work for Goofy's Thanksgiving Dinner!! It is a special day, but she said the price is still covered by the voucher. YAY!
Have fun!
Kriss
You might get a quicker answer from Getaway Today but I would highly doubt they would work since the vouchers are pretty specific to Goofy's Kitchen and the other one for Character Meals.