I love Fusco. Yes, he started out a dirty cop, but through his work with Team Machine he started feeling good about himself again, and wanting to be good again, and he did change. His part is small, in terms of screen time, but I have seen real story and real growth.
I often think Reese is too short or gruff or just rude to him, and since I usually love Reese that bothers me. But I do think he is coming around, At least the others (Finch, Carter before she died (sniff) and Shaw) seem to value him.