Pro-style is such a broad term. But I think people mean it to describe a balanced offense, and less about certain formations. There is a lot of truth that Nebraska leaned on the run game during it's most successful times. But I also think they were slightly more balanced than people give them credit for. The 70-71 teams didn't run much QB-option (maybe 5 times a game). They even ran some no huddle offense, which is certainly Pro-esque. I'd say they were a very I-formation team. In the mid-70's they had a QB that started in a SuperBowl, one Vince Ferragamo, but they weren't as succesfull those years, getting killed by the Wishbone Oklahoma teams that rarely every passed the ball. Again, I have to admit the importance of the run game on the plains (looking at you too Oklahoma). That pushed Nebraska to look to adding the option game from many formations. Nebraska really only ran the option 15 times a game in it's heyday. It was way more power run than anything. And it's philosophical approach to option football was that it was much like a pass. Chances are it was for little or no gain, or a very big gain with a slight elevation in turnover potential. Viewed in that light, under Osborne were are looking at a close to 60-40 run-pass offense. Not quite as lopsided as one might think.
How this relates to Mike Riley? I think he will learn the importance to the run game. He's very open-minded and I have looked his teams over. He does very well at playing to his teams strengths. Given that Nebraska has mostly only mobile qb's, I think you will see "some" qb running built into his jet-sweep scheme. I base that, again, on his history of adjusting to talent, his comments he made while still at Oregon St about need to change things up, about OC Danny Langsdorf comments about learning from Russel Wilson at Seattle and how that run-game killed the Giants, and the fact that Nebraska is actively recruiting QB's that aren't strictly pro-style.