I don't think Forrest and Lee were in the same boat when Forrest was testifying before Congress. Lee kept to the letter of his parole and had nothing to do with any organizations of any sort, so there was no need to question him. Forrest, however, had a friend in Congress who made sure his name was mentioned - Brownlow. Brownlow had been fighting the klan as governor of Tennessee for a long time and knew Forrest was in with them. At any rate, with or without his fifth amendment rights, Forrest wasn't about to rat anybody out or hang himself. He wasn't pushed too hard about it, either - hanging a general of Forrest's stature would have lit the South on fire, which was something even the most radical congressman didn't want. Brownlow figured as much but saw it as a good tool for squashing any political ambitions Forrest had - the last guy he wanted sitting next to him representing Tennessee was N.B. Forrest.