I need to grease a baking pan (which I don't have) for brownies. I also don't have butter or shortening. I do have one of those pyrex oven safe glass pans and something like a small dutch oven, but with a glass top instead. Could either of these substitute for baking pan instead? And in lieu of the butter, could I use vegetable oil and a paper towel to grease one of the pans that I do have (without affecting the final results of the brownies)?
Vegetable oil will be fine - that's what's in commercial nonstick spray oils anyway.
A pyrex oven safe glass pan is a baking pan. The baking time might be slightly different than with a metal pan, but it will work perfectly fine. Just make sure it's the same size pan the recipe called for, or scale the recipe to match the area - if you change the thickness, the results are going to change.
The dutch oven (uncovered) would also work, though it will take a lot longer to heat up, so it will probably affect the baking time substantially, and you may have to be careful not to overcook the top.