I'm not an attorney, but been dealing with this issue for a very long time.
I work in a white collar environment, and employees are either "exempt," or "non-exempt." Supervisors and above are exempt, and everyone else in non-exempt.
Exempt employees are strict salaried, and will make the same salary if they work 35 hours, or 50 hours, etc.....however, I do want to say that if a salaried employee abuses this, and consistently fails to work 40 hours, this will absolutely become an issue with them.
Non-exempt will absolutely be paid time and a half, if they exceed 40 hours, whether it was approved or not......however, this will become an issue with them, if they worked OT, without prior approval from a supervisor or above.
Lastly, as far as designated holidays.....if a non-exempt employee works on a holiday, they will be paid time and a half for each hour.......but, as stated earlier, this will become an issue, if they worked it, without prior approval from supervisor or above.
If an exempt employee works on a designated holiday, he/she and their direct manager will figure out a fair way to work in some comp time.......never a big deal.
There's really no valid reasons for employees, at any level, to get all pissy about stuff like this.....unless of course they're being taken advantage of.