Regular olive oil is a good choice for sautéing vegetables--it adds a mild olive oil flavor and can stand up to higher-heat cooking. It also coats the barley grains so they don't clump. Try other summer vegetables in this satisfying side dish, such as corn, zucchini, or even lima beans.
I found it took far longer to cook the barley and get it to an appropriate risotto texture than the recipe indicated. The veggie blend was quite good - I might use that in a regular risotto but I probably won't make this recipe again.