The supposed constitutional prohibition doesn't make sense. While I suppose a state can put what it wants into its constitution, it would be highly unusual to put something like that in a constitution.
So...go to the source and read for yourself. Here's a link to the Nebraska Constitution. http://www.neded.org/files/research/.../nebconst.html
There is a section that deals with the general control of the U of Nebraska but in a quick read-through, I saw nothing addressing sports. Go to CVII-10 in the Nebraska Constitution.
These message boards (not just Bisonville -- ALL message boards) may be the most efficient method of spreading false information yet invented by man.