Not plants, but Matt Abbatacola's (Bernstein wannabe JR.) has a simple job, screen out everyone who isn't a mouthbreathing boob. that's the whole bit, anyone who has brain cells who calls, unless they agree word for word with Dan, aren't let on the air, and if they pretend to be a dumbass, to get past Matt, the second they go off script, they are muted, talked over, and hung up on.
The whole thing only works with Dan being the smartest man in the room, as soon as he isn't, the whole bit falls apart. Which is why I turn them off as soon as they start taking phone calls, once you know the bit, it isn't funny anymore. I don't mind Dan's monologue opinion bits, or the guests that they have on weekly ( and not the fan guests, the actual paid expert guests, I don't care to listen to a senile old **** review a movie, it was funny, the first time, now it's sad. )
Basically, he doesn't want to actually have a conversation with anyone who might possibly be his equal on a subject. Also, I don't think he gives much of a shit about anything other than his son's hockey HOF career, and basketball. Actually, I don't think he knows a whole lot about other sports to be honest.
TL;DR He's entertaining in very very small doses. And it's all a bit.