Do they some particular trait that makes them suited to it?
Don’t know, but they make for a great animated movie.
Dalmatians were bred not only as firehouse dogs. They were bred to keep other dogs away from draft horses in general. That’s why you see them with the Anheuser-Busch Clydesdales.
What it boils down to is they were good horse-babysitters, but you can read the short article here:
https://www.msn.com/en-us/lifestyle/lifestyle-buzz/this-is-why-firehouse-dogs-are-usually-dalmatians/ar-BB13VTsl