"At American Express Travel, we verify upfront during the booking process if the Card Member is eligible to receive the benefits"
This definitely suggests that provided the relevant checks are 'passed' during the booking process then booking for friends and family shouldn't be an issue.
A recent example of a FHR booking that I saw, made for people other than the cardholder, makes no mention of who the cardholder is so I'm not sure how the hotel would be able to ascertain whether the person checking in is the cardholder or not unless they have a more detailed reservation to hand.
It seems we still don't have many/any definitive answers to the main query in this thread though...