given that it's a batter, how much does the blending affect the cooked texture, out of curiosity? have you tried powdering the oats dry, first, before attempting to make a batter with them with the stick blender?
obviously a different price category but this is something i'd probably turn to the vitamix for. incidentally, if this batter is the main sticking point, you might be able to just purchase pre-ground oat flour and use the bamix for everything else.