RE: the crowd
I don't think the crowd isn't reacting, most likely the circular stage means that you can't have multiple monitors on stage cause they would pick one another up... don't feel like explaining the technical of it but basically the sound man is turning the house sound up about every couple bars to pump the crowd reaction through when he thinks the rappers are gonna pause in their flow, but if they are still going he doesn't.
So the crowd is still reacting... but whether the reaction is sent through the board varies.
Also, most likely the stage mics have priotrity over the house pick up so even if he pumps the house through- if say Lux is yelling and the decibals on his mic are say at 7 (of 10), then the crowd comes through at 3 max to not pop.