Undergraduates, like almost every student-athelete, do not receive stipends, though.
No, but in reality undergraduates generate very little useful scientific data on their own. Without graduate students there, most of their experiments wouldn't be completed because they would never have received the appropriate training and usually lack the free time to complete all of the minutiae in a timely manner (usually due to time constraints imposed by class). It is typically grad students or post-docs who do the hands-on training, as the faculty member running the lab usually doesn't have time to teach someone how to do the bench work (at least in biomedical sciences; their time is completely occupied with all of the other tasks required to keep the lab up and running).
So in the end, it's another comparison that doesn't quite work--which isn't all that surprising as collegiate athletics is a unique beast unto itself.