Hi Corinne,
If he is dribbling urine or prone to recurrent dysuria, Saw Palmetto will likely help. Even if the prostate is healthy, as it addresses the urethrospasm you think you're seeing. I'd use the NPHC version and give robust doses. It's tasty so he shouldn't mind. At least half a teaspoon twice a day or even more often.
Bu Zhong Yi Qi Tang is another formula to consider when the main issue is an issue with smooth muscle tone. It also addresses recurrent tendencies to cystitis. If you paired it with Xiao Chai Hu Tang, you would unbuckle the Dai Mai as well. The two formulas would then act together to relieve Stasis in the lower burner (with or without the continuation of SFZYT).
This approach fits the toned pulse you're seeing and the fact that the dog is raw fed. Unless a dog is very Spleen deficient, real food diets tend to not be Dampening. Any time a dog fed raw long term has issues, it raises the chances that a Shao Yang disharmony is at the bottom of it.
How could it cause cystitis? Well, if the plant material is missing entirely, then so are carb-fermenters in the gut, and they produce the propionate that regulates the immune system - against both excesses as well as deficiencies of immune function. If the raw diet she is feeding has no plants, that is very likely the problem unless this is a Damp dog to begin with, but where the raw feeding cured the dog's Damp tendencies. And if that happened, then there would not be cystitis now.
Hopefully, that makes some sort of sense. Let us know how things go!
Steve