Could you provide the exact quote? I saw an article on this site that recaps a radio interview where Riley says fans played a part but I don't see him say specifically in social media. I ask because while the NCAA pretty much has less than zero power to stop fans from reaching out to recruits (they'd basically have to bust every school for that) having the program encourage it is a different story. In fact, over the past few years a lot of programs have sent out a warnings to fans/boosters not to do it (not that they think it will stop it but at least they can say they said something and trying to comply with the rules).
What you are suggesting is a NCAA violation. Again, the NCAA is going to do nothing to stop it...well unless they find proof the program itself is doing something to encourage and/or enable fans to organize and recruit on their behalf. I can see how you might read into the quote I just saw and think he meant social media...maybe he did...maybe he just meant something like the way fans supported the team at your spring game really showed recruits how much you guys love NU. All, I'm saying is you might want to be a little careful on this one.