Clarett is probably done with school. He napalmed his bridges with OSU. The NCAA will bend over backwards to keep him out of college at this point, after everything he's done. The CFL makes sense for him (BTW, Pink Dove, you forgot Rocket Ismail, whose decision to go to the CFL over the NFL turned the entire draft on its ear).
Williams is a different story. He relied in good faith on a court ruling. The NCAA will probably take a hard line, but I think the door is at least open a crack, in part because Williams' action was entirely reasonable. As for the supp draft? Tough call. The NFL probably wants to avoid creating any uncertainty with their "3 years out of high school" rule. As such, they could take a hard line on Williams, but in his case, the supp draft is at least a possibility.