Guys, it's very possible that the term "regular" is being used loosely here. I mean, Wendy and SuperDave on Vegas are considered regulars, but they are not in the opening credits with Marg and the others. They are the first names shown when the show comes back from its first commercial break though. Perhaps Eddie's character would be like that. Wendy isn't always on the show. And sometimes when she is, she doesn't have that much screentime. SuperDave is on average, in one scene per ep (the examining the body at the crime scene because Doc Robbins doesn't go out into the field that often).
Secondly, this guy is supposed to be a detective. they've already done the whole CSI dies replaced by cop turned CSI on this show. Surely they won't do it again. If anyone leaves for the new guy to take their place it would most likely be Frank. But, no one necessarily has to leave for a new character to come in. Like I said, its possible he won't be a regular in the sense that David C and the others are.
I still say its possible they might do a cop-turned-ME storyline. That hasn't been done before. they did ME turned CSI on NY and kind of with Ray on Vegas, but never a cop first then ME. It's possible this guy could be someone who started out wanting to be a doc so he went to medical school, but then maybe someone he cared about deeply was murdered and that made him want to be a cop, so he went to the academy and became one.