Police dogs are trained to rat you out, either legitimately or illegitimately.
Them being victims who weren't given a choice doesn't make them not active participants, just sympathetic ones.
Like modern pirates. They're doing it because they need to feed their families and often have no real choice, but that doesn't make it okay to hurt random fisherman and freighter crews.
Police horses will do their best to not step on you when forced to ride into a crowd. Not bastard.