I asked my slot hostess at Caesars Palace whether it made a difference if I booked through her or on-line, she indicated it didn't make a difference.
In the MGM system (apparently) it does, my slot hostess at Mandalay Bay said she gets "credits" when she does the booking, ditto for Monte Carlo.
Interesting. When I use to book stuff through my hostess from Caesars, she always told me to tell her any of my friends that were coming with me that had a TR card. She told me that she would get credit for them even if they don't book a room but just use their TR card.