Jason, Chuck and I have seen them down there, live and dead. The DNR also acknowledges they are there as well. You are right in that they are hard to tell apart though. The Bigheads aren't nearly as acrobatic as the silvers.
You gotta be careful with the DNR guys. They arent always the best with fish ID. Heck the last time we got stopped I asked him what species of sturgeon we can keep, his response was that he didnt know there were more then one!