The field condenses in the redzone and more importantly on the goalline. When you are going to be running many times anyway due to the passing windows shrinking, a running threat at QB to add another eligible player the defense has to account for rather than possibly risking injury to Raiola is something I really like. Further, Haarberg is more than a wildcat RB playing the position, he has a much better arm than an average wildcat insert.
It also gives the defense other things they have to prepare for, one of the many reasons that teams like Oregon run the swinging gate PAT attempt. They run maybe one play a game out of it, but the defense has to spend much more time getting ready to defend it. With practices limited by the NCAA, that's another leg-up we can have.
For Nebraska, they already installed the running packages for Haarberg last year anyway, so you aren't introducing anything new. In regards to your last sentence, what if we leave Raiola in and he throws a pick? How many people would be screaming to just do a QB sneak or run the ball?
There's a time and a place for HH at QB IMO.