Would never book a place with a compulsory X-Mass or New Year Dinner , as I usually go to Crustasian's place for Christmas nosh and am too busy celebrating at New Year to bother with food.
It does seem to be a way for some of the hotels to increase earnings over the holiday period, it would be easy enough for them to have an option at time of booking whether you do/don't want to partake. How would they stand if you said no ,"because of religious grounds".