DC has been on the State's witness list for a long time now and as others have pointed out, the State did an investigative interview with DC and the defense could not be present because they refused to put him on their own witness list.
I don't think the State ever had a reason NOT to use DC as a witness. The mere fact that he was out there in those woods searching for a deceased Caylee (slashing through black trash bags) is reason enough to call him. It's an added bonus that it is all on video tape because I am sure the jury is going to be disgusted watching this man, who works for the Anthony family, trampling, poking, proding and being completely careless in his search for this poor baby.
I won't get into all the emails between DC, Luke, and Ginette... but there is enough evidence in those emails to make a jury doubt the story Dominic gave to LE about his reasons for being out there.
Another reason I think he may have hurried up and got another lawyer was because Jeremy Lyons knocked at his door. He did just get another 300 investigative hours.