Remember, the anonymous source and the unnamed person who supposedly informed Tressel are different individuals. So the source need not have OSU's best interests at heart, even if the person who first attempted to get Tressel's attention did/does. That said, I'm cautiously optimistic. Unless Robinson and Wetzel have something more up their sleeves, something they're ready to pull out when OSU releases the obligatory press statement denying all allegations but insisting that they'll conduct a thorough investigation in-house -- that is, something like multiple corroborating sources or a paper/email trail that leads to Tressel -- then I can't see the NCAA being able to prove anything besides one person saying that another person said that s/he told Tressel and that Tressel seemed concerned.
Of course, some damage has already been done (though obviously not as much as could be done). Often no one remembers whether allegations are true or not, simply that they were made.