Can an employer choose to deny exempt employees' holiday pay?

In a word, yes. That is, holidays, like other paid time off work is a gift from employers. If the employer determines that s/he cannot afford this gift or that the employee(s) does not deserve this gift, s/he can withdraw the gift.

Now having said that, exempt employees are required by the Fair Labor Standards Act to be paid for any day in which they perform their work--even if they work less than 8 hours.

Employers should also be careful about deducting pay for time taken off work for jury duty, witness appearances, temporary military leave, disciplinary infractions or lack of available work unless the deduction extends through an entire pay period.

Department of Labor regulations specifically allow daily deductions from exempt employee wages only for sickness, disability and personal leave (including vacations).

It is certainly not a good employer practice to refuse to pay exempt employees for defined company holidays. Morale must be affected in such an environment.