You'd have to soak them overnight, or people would break their teeth. Then you have a wetter batter. For muffins, I think it's not a good idea to make the recipe as is,but you could experiment and leave out some of the recipe's liquid.
Do you have quick (not instant) oats? They'd be a fine substitute for rolled oats in muffins.

You'll have more success if you find recipes that use steel cut oats rather than substituting it for rolled oats. As cloudy christine pointed out, steel cut oats are real teeth breakers.

Check Bob's Red Mill for recipes (see link below). Click on RECIPES.

You can substitute COOKED steel cut oatmeal cup for cup for COOKED oatmeal in a recipe, but it's not the same thing uncooked and will not substitute cup for cup as a dry ingredient.

-Grainlady

Here is a link that might be useful: Bob's Red Mill

Thanks for the info. I wanted to make the recipe lower in glycemic index, but definitely not tooth-crackin' unfriendly! So I'll use what the recipe calls for...rolled oats.

Why not use Old Fashioned Oats instead of the Quick Oats? You would have more fiber and lower glycemic index than the Quick Oats, but won't break your teeth like on the steel cut.