People, especially exempt employees, may work on their vacations, so it is legal for an employee to use vacation time for work time and your district managers may allow this. That is, no law says that someone may not work while on paid vacation, and it is actually not all that uncommon, at least in the NY/NJ area where I'm located, for salaried exempt employees to perform at least some work while taking vacation days. Similarly, exempt employees could work on their nominal days off, holiday days, after  or before hours, etc.