With fpv racing a racer wants an experienced pilot as their spotter preferably another fpv racing pilot. That person will be familiar with the course, and will know and understand the specific race rules ,how things work and are run. A racing pilot,in my opinion, would not want someone from the audience or the sidelines spotting them..............it just wouldn't be good for the pilot and it wouldn't be safe.
Again, as far as mgp, I believe it is a tightly focused group based solely on fpv racing where pilots set up, run, and participate in their races. Yes some may bring a friend or family member to help set-up but I doubt they are members. With the way ama qualifies a sig those folks could be members but I don't think many if any non-flying friends,family members,wives,husbands, etc are joining mgp.
If they are I don't see how mgp is breaking or can break that down to satisfy items 2 & 4 on the ama document to qualify as a sig.
http://www.modelaircraft.org/files/158.pdf
Perhaps like many things with the ama, this sig qualification document is outdated and needs to be updated.