I just got off the phone with the meeting sales rep. It seems I can either earn the normal points on up to 3 rooms for the stay or earn 3 points spent by everyone in the party (and Marriott will help me figure out which one will allow me to get the most points.)

So it looks like Marriott doesn't let you "double dip" for both the "planner" points and the stay points. But he did say that if I stayed there, I could get "night" credits no matter which way I decided to earn points. So at least I'll get a couple of nights for the stay plus probably the "planner" points.