I didn't notice any dugout challenges; it was always the batter, who presumably had only a short period to challenge. I can't imagine that the dugout or clubhouse was involved given how fast all the challenges were.
I was surprised there were as few challenges as I saw since every batter could challenge once per at bat, and there was no penalty for being wrong (other than not being able to challenge for the rest of the at bat. Seems like nearly every hitter in MLB complains about a pitch in almost every at bat.
By the way, my recollection was that about half the challenges succeeded.