Stir water and chia seeds together in a bowl; set aside until thickened, about 10 minutes. Add enough hemp milk to thin chia mixture and transfer to a blender; blend until smooth.
Combine spelt flour, millet flour, baking powder, baking soda, and salt in a bowl; stir in chia mixture until batter is well mixed. Fold blueberries into batter.
Melt butter in hot skillet. Drop batter by large spoonfuls onto the skillet and cook until bubbles form and the edges are dry, 3 to 4 minutes. Flip and cook until browned on the other side, 2 to 3 minutes. Repeat with remaining batter.