Does a date fall in a date range (between start and end date)

Hi

3 tabs:

1. vacation: form > start and end date vacation + linked records to “employees” so they can select themselves

2. employees

3. projects: per record 1 day to work on a project + linked records to “employees” to select technician

Question: is there any way to signal in any way (preferably not being able to select the technician in question) that the selected/to be selected technician is on vacation on the workday in question?