This is verbatim from the Staff, Family and Friends website:
"For Hilton Family Travel Program rates:
If you have booked the Hilton Family Travel Program rate for family take the Confirmation Number to your Human Resources Department or General manager, and obtain a signed Hilton Family Travel Passport. The Hilton Family Travel Passport will identify your family as they check in at the hotel, and ensure they receive the correct rate for their stay. If you have made the reservation for yourself and have an Esprit/Hilton Club Card then you will not need a Hilton Family Travel Passport you simply need to take your Esprit/Hilton Club Card with you when you travel and present it at check-in."
...and yes, the Front Desk really do control your eligibility - if you can't present your 'passport' they may change your rate to the BAR for the night.