You could argue that a really good debater should be able to argue both sides of anything.
As I had always been taught about debating, you
are supposed to be able to argue either side of any issue. It's all about the art of argumentation and not about the issues themselves.
Having a YEC argue for evolution and an "evolutionist" argue the YEC side would be interesting. I would anticipate that the YEC's presentation will be filled with gross misinformation and warped misunderstanding of what he's arguing for, based on his already existing warped misunderstanding of evolution and science. I anticipate that the "evolutionist's" YEC presentation will be filled with lies and deception and thus be indistinguishable from a real YEC's presentation of the same.
One mistake that I anticipate an evolutionist playing YEC would make would be to take the claims too seriously, in which case he may try to analyze them and present a too lucid and detailed account of the claims. Even worse, he may be more likely to allow himself to be drawn into discussing and defending the claims, something that real creationists know to avoid at all costs.