Yes, it was said that he would get extremely irate when Greb's name was mentioned as a fellow dirty fighter from Pittsburgh. Late in his life he softened, and said that he wasn't even the dirtiest fighter in his neighborhood, as Greb was from right up over the hill from him.
Zivic thought Greb to be the greatest fighter of all time and cited his creative use of illegal tactics as one reason.
Zivic: I'm the second dirtiest fighter of all time? The dirtiest? Harry Greb. If you lifted your shoe from the canvas, Harry would bite it.