Yes, you can eat polenta. It is counted as a grain.
4 oz. = 1 grain serving
Masa (also known as ground hominy) is flour, so it’s not Bright Line Eating friendly.
Whole hominy is corn that has been dried and treated with alkali. It is counted as a starchy vegetable.
2 oz. dried (6 oz. hydrated) = 1 vegetable serving
Corn meal is usually used in combination with other flours for baking. As such, it’s not considered to be Bright Line Eating friendly. If you have to use it as a coating on something you’re cooking (without any added flour, of course), it would count as a grain.