Whatever might have gone down in the 90s to my knowledge has never been brought to the forefront as far as any steroid use goes.  Personally I don't think there were a lot of players that used them if any.  I know creatine was a big part of their strength and conditioning program.  A lot of the dirty laundry that was happening off the field was talked about in detail in a book called Unbeatable by Tom Shatel of the Omaha World-Herald.  Steroids and cheating were never addressed in that book and that would have been the place to do it if it did occur.  Really terrific read if you can find the time or care to do so.

What did change that I think made it significantly harder for Nebraska to make things work was the elimination of the "Prop 48" players.  Osborne took all kinds of kids from troubled childhoods and off the streets of big cities to come be part of a family at Nebraska.  Those guys came to NU where they were accepted, embraced, and supported by Osborne and their teammates in ways they never could anywhere else, but still played with the grit and "smoldering fire" in their guts that they had instilled in them from their childhoods.  Osborne and his staff harnessed and channeled it into the attack and destroy mentality that the Huskers could display on both sides of the ball in most instances but there were negative outcomes with it too.  See Lawrence Phillips.