In my experience, It is very possible to receive night credits for up to three rooms. Be sure that if you're reserving the rooms, that you add the other people's names as GUEST #2 or book each room separately and position your name as GUEST #1 and the other person as GUEST #2.

As a matter of fact, I 've booked 3 rooms for other colleagues who have attended conferences. I wasn't a part of their trip and still got nights credit and points credit for up to three rooms.