The investigation is looking at a group called Life Surge which is a Christian "wealth training" group. They hold seminars around the country and use celebrities to speak and endorse them. The are accused of using high pressure sales techniques to sell sketchy "wealth creation" training courses and materials. Tim Tebow was a prominent backer of them but has backed away since the investigation began.
As for the OSU players, they aren't accused of doing anything wrong. When Life Surge held a seminar at OSU, JJ, TSC, Caleb Downs, Herbstreit and Urban all appeared and spoke. Apparently Urban helped secure the facility that was used. OSU has already said that none of those guys did anything wrong or broke any rules. More than anything, it's just kind of a "bad look" situation.