Possibly, if the quick cooking ones were soaked first, you could use them in bars. First priority, don't break your teeth!

I think that for granola, the steel cut grains are too hard as opposed to the rolled oats

You could try using them for homemade granola bars (they might be too small for granola, but with granola bars they'll bond together so that would be less of a problem) or you could use them in some other powerbar type recipe.

I think rolled oats are a better bet for granola. I'd use the steel cut oats for oatmeal!