The bragg’s contains cane sugar and honey, which isn’t beneficial do the diet. However the servings size contain about 4g of sugar, so it shouldn’t set you back that much. If dressing gets you to eat salads more often, then I feel that you should go for it and not worry.
I don’t see any harm in eating buckwheat, so go for it if you want to! It does contain 25% starch, but its quite a bit less than rice, etc.