We are all different. I can eat buckwheat only rarely. Buckwheat is technically not a grain and it has no gluten. But it does raise my blood sugar, which is not good for candida.
If you have candida, sugars and starches feed candida. This means all carbs, including fruit. It all depends on how bad you want to get rid of the candida how strict you are on your diet. There is a big difference in having buckwheat once a month or even brown rice once or twice a month and having a starch like buckwheat or rice every day.
Some may only need maintenance and can have a little more grain, but with active frequent yeast problems, or a family history of candida or diabetes, I would be really strict and take lots of probiotics and Colloidal Silver to help my body get rid of it.