Truth be told, Z-Nation has taken their characters in much different directions than their Walking Dead counterparts.
The Rick Grimes expy is spoilers:end of spoilers
dead .
The Michone clone (didn't mean to rhyme) is spoilers:end of spoilers
the leader
The Doc character isn't really that much like Hershel. Hershel was the heart/moral center (much like Dale was before him) of Rick's group. Doc is mainly comic relief.
Murphy isn't much like Shane. Shane was an alpha male bucking against Rick's leadership. Murphy (until recently) was far from an alpha male. Basically people treated him like property and he usually put up with it out of fear. The only thing he had in common with Shane was that they both are amoral (or maybe immoral).