When Saddam was about to be executed, the men that were surrounding him chanted "Muqtada" several times?

Yes the Elder Sadr was hung in the exact same gallows. That is why they said that. The elder Sadr was a Grand Ayatollah and Sayed (decendent of Muhammad) . The Shia don't have one great leader and Grand Ayatollahs are of the highest order. He was considered a man of peace that did a lot for the poor Shia in Baghdad especially Sadr City (thats why its named after him). Actually Muqtada failed out of religious school and has very little religious training but is still considered holy by some Shia because he is obviously also a Sayed. He was thought of as kind of a black sheep in his family but has been able to capitalize on his fathers name as well as ancestory to gain a following. It can be very profitable to be part of his mehdi army providing jobs to the poor even though it takes advantage of other poor Shia that are loyal to Sistani in Najaf and other clerics. People use there affiliation in the mehdi army to recieve aid and get jobs just like people did when they joined Saddam's Baath party.