As always video helps:
Baseball Video Highlights & Clips | MIN@KC: Gardenhire gets thrown out for arguing a call - Video | twinsbaseball.com: Multimedia
It most every game that I have worked my partner and I have pre-gamed that if the BU sees the ball hit the batter in the box to kill the play immediately. I don't know if that is correct (good idea) or not, but if the crew has it set that way then Vanover wouldn't need to check with Reliford, because Reliford would have killed the play then.
I don't know how the announcers "know" that Reliford wants to help out on the call. It doesn't look like he standing there yelling, "Ask me, ask me, ask me!" but what's new when it comes to the TV guys.