Could I use something like this to put a 90 degree bent in them?
As Graphus said, yes you can, but a good vice can work just as nice.
I've used a vice on 1/8" x 1/2" stock to make bands for trunks. That is surprisingly easy to bend where you want. 2" wide will take a little more work, but should be plenty doable. I also agree that a larger hammer works better.
Now, a word of caution on the brackets. A plain 'L' bracket without a strut for support will likely cause you a lot of pain. The first problem is the shelf will likely be bouncy. The next is if you are putting a lot of weight on the shelf it will slowly bend the 'L' down until it drops stuff off onto the floor. It might take a little while, maybe even years, but it will happen, that's gravity for you.
However, a simple fix is to make a brace from top to side. You could do extra metal work to bend a triangle, or take a piece of oak, and cut it to fit, then just screw the wood to the bracket, you don't even need to go from end to end, just a couple inches from the corner on each side should do.
Below are brackets commonly used for shelving brackets, they have 'triangles' for strength.