Yes.
Was he obligated to take the case? Would it have harmed his career if he hadn't?
Obligated? Probably not. But when you're a junior partner at a law firm, do you say "no" to a senior partner who asks you to lend a few hours (I've read 6 hours was the extent of Roberts' work) assistance?
Again, if it were not donated time, then I could see it. But I want to know why these people received free legal services, AND why Roberts was willing to give of his valuable time. Six hours of his time equals quite a large cash donation to the cause. They are entitled to representation and a fair hearing, but no one has to donate their servies.