I see it being a big risk. In some situations it could be really good to tell a kid (and parents) that they will a scholly for years no matter the situation. On the other side, it hurts the program with the inveitable of losing a certain percentage of your recruiting class, and not being able to replace the prospect.
For Nebraska, I could see it killing the walk-on program. If your big pitch to give up a scholly to UNK, NW Missouri St, SDSU, etc is that if you work hard and get on the field that in 2-3 years you could be seeing a scholarship. If you have all your money tied in multi-year scholarships, there will be none to give walk-ons.