In re: requesting to see (or get a transcript) of what your counterpart , whether it is a politician, corporate executive, etc., has submitted for something like this is standard PR practice. Sometimes the requests are honored, sometimes they are not, but requesting them is hardly unusual or indicative of anything. In fact it would be unusual not to ask for it. From what I understand from colleagues who work on the show McCain and Clinton initially had the same stipulation, and none of the "balked." There's smoke but no fire here, OP.
In re: "stooping low" - if one of the 3 Presidential candidates made an appearance on "Your Momma Don't Dance" I would concur. However, appearing on a prime time variety show that consistently gets the highest ratings on American TV after the Super Bowl and the Oscar telecast is smart. Especially when it's an episode dedicated to a global relief charity and populated with guest appearances by a whos-who of international entertainment superstars. It's about face-time with the largest audience on TV, including a substantially higher share of the 18-49 demo versus any show that competes against it. Clinton, Obama and McCain would have been foolish to decline the invitation.