The only time I have ever experienced a hernia was with one of my dogs... She got it taken out a few months ago and she still has a little swollen spot that looks just like the hernia did, where it is healing. I don't think it is as painful for dogs though. :/
My guinea pig got one. His testicle grew fuckin massive, though it didn't pain him, the skin kept drying and bleeding. We got him surgery, though successful, it died from shock.
I never really notice them in adult dogs. My mom has been breeding pugs for over 25 years and you usually only see them in young puppies, always in the middle of the stomach area.