I guess the Reservations person might not come into contact with guests in the same way the reception team too (we’d call them Front Of House). They could and often do their job from an office out of sight, dealing with bookings that have come in.

Every hotel is different, so it's best to check with the hotel that's recruiting, to see the list of duties expected from that employee. But based on the name of the role, a receptionist is focused on greeting customers, being their first point of contact; while a reservation clerk's role would be primarily making sure bookings are processed fine. So in some hotels, the receptionist may greet the customer and then handle their booking too; while in other hotels, the receptionist may greet the customer, then upon finding they need help with a reservation, hand over the task to a specialised reservation clerk to solve it.