Although Sandman has appeared in the ultimate Universe, his character has not really been expanded or touched upon in a meaningiful way. Should Ultimate Sandman have the same characterization he has in the Spider-Man 3 movie:
In the Spider-Man 3 Sandman commits crimes in order to get medical attention for his daugther who suffers a number of diseases that threaten her life. In the Ultimate Universe, it could be "revealed" that Sandman that Flint Marko volunteered for the experiment that turned him into the Sandman because he was promised a large amount of money in return. instead Justin Hammer had Marko locked up and treated him like a lab rat. Similarly he joined the Ultimate Six not only get revenge on fury, but also to get the money Osborn promised. While he was imprisoned, Flint's wife was taking care of their sick daugther, working 3 jobs to support the barest requirements of the medical treatment their daugther needed to survive. However Flint's wife has recently died in a car crash and Flint is the only one left to care of his daugther, so he escapes from prison to commit crimes to support his daugther. He has bares some ill will to towards Spider-Man, who he somewaht blames for his inability to get the money needed for his daugther's medical treatment and for imprisoning him away from his family (he feels guilty that his wife died while he was in prison.) this would give Ultimate spidey a tragic foe, something he has been missing in the Ultimate Universe. It would nice change of pace if Spider-Man had a villain he felt sorry for.