I set up a list based off of a calendar, this is a list of tickets we have available to employees, I have set it to not allow an employee to sign up for more than 1 set of tickets, is it possible to "lock" that cell that holds the employee name so that no-one may go in and overwrite that?
Out of the box, you can't lock a cell.
Lookup column linking to another list would require a good amount of work. You'd need to create a list with every employee (keep it updated), apply read only permissions to the list, and grant read / write to admins. The Person and Groups column type cannot be used as a lookup source, so you'd need to use the Title column or a single line of text column type.