That's... kind of the gag, there. That they all pretty much look alike?
Point one: The guy in the latest comics isn't necessarily "Luke". It's a reasonable guess, as hes' the only named dalmatian in the cast, but it's already been long established that there's more than one on the force.
Point two: It doesn't matter who he his. I didn't bother having his name mentioned in the strip because he's just a walk-on. He's one of the guys from the FD, that's all that matters.
Point three: None of them really had names until today's strip. The only other FD personnel who had been named were some random names shouted by Sarge as they were dismounting to attack the fire. We don't know who he was calling "Hicks" and Hudson" and all that, and there were a couple of cats and other dogs in the zombie series, but really, it was never my intent to have too many named emergency personnel.