You know Johann, at first, I believe it was for his message, just as with Billy Graham. However, in the 80's when he went a bit left with the " I have to raise this money or God will call me home" thing seemed to change people's perspective. After that you saw a gradual move to place his son in the forefront. In fact, I believe Oral was off the air for a bit after that, and I remember other televangelists(Jerry Falwell, etc.) being asked about it and saying that he needed prayer.
As to George's OP, yes anything is possible with man. As long as man establishes these ministries, even under the guidance of the Holy Spirit initially, they are always subject to the infallibility of men. Most have the best intentions, and then yield to one temptation or another to varying degrees. Large ministries such as oral Robert's, even GC, have to be "business" at a certain point. It is, however, fine line that they walk between "business" and the "The Father's business of ministry"
Good news is that God knows this and their hearts even before He impresses them to establish a ministry. Just like he annointed David to be king knowing ALL of his failings and moral weakness. As the song says, "He looked beyond my faults.............."