If you prefer a smoother texture for your muffins, then yes, you can blend the mixture before baking. But, you will likely have to add a splash of milk to help blend the mixture to a smooth consistency. I did try this method during my recipe testing, but I found that the muffins lacked texture and became a little too dense for my taste. By keeping the oats whole, the muffins will have more texture and it will prevent them from becoming super dense.