I also like to use spent grains to make dog biscuits as well as throwing them into a loaf of bread. The first time I used them to make bread I went with way too much spent grain. The bread came out very dense, which was OK, but there were way too many grain husks which made the bread very coarse and scratched your throat on the way down. Now I run the grains through the meat grinder attachment on my stand mixer before using them, even for dog biscuits. For bread, I swap out the spent grain 1-for-1 with flour, then adjust with water or flour after kneading for a while to get to the proper dough consistency.
As for taste, I find the base grains add little to no flavor. I keep meaning to save extra wort to use instead of water in the bread, but I either never end up with much extra wort, or I just forget.